> ## Documentation Index
> Fetch the complete documentation index at: https://docs.getthread.com/llms.txt
> Use this file to discover all available pages before exploring further.
# Phone system forwarding directory
> Where to find the call forwarding setting that sends calls to Voice AI, with links to each vendor's own documentation, for RingCentral, Microsoft Teams, 8x8, Zoom, Cisco, Mitel, 3CX and other phone systems MSPs run.
Voice AI joins your call flow by **call forwarding**, so the setting you need already exists in your phone system — Thread doesn't replace it. This page names that setting per platform and links the vendor's own documentation. It deliberately doesn't reproduce their steps: vendors change their admin consoles, and their docs are always the current version.
Read [Forward your phone system to Voice AI](/ai-agents/connect-your-phone-system-to-voice-ai) first for which Thread number belongs where. In short: your support number forwards to the **Attendant** number, and a queue's no-answer or after-hours rule forwards to the **Overflow** number.
Vendor links and setting names were verified in September 2026. Admin consoles get renamed — if a label below doesn't match what you see, the vendor's linked documentation wins.
## Cloud phone systems
| Phone system | Where to set it | Watch out for |
| ------------------------------ | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| Microsoft Teams Phone | Call queue → **Exception handling** → **Overflow**, **Call timeout** or **No Agents** → redirect to an external number. [Microsoft's guide](https://learn.microsoft.com/en-us/microsoftteams/aa-cq-setup-call-queue) | Needs Pay-As-You-Go or Communication Credits — [see below](#microsoft-teams-needs-pay-as-you-go) |
| RingCentral (RingEX) | Call queue → **Call Handling & Members** → **Wait settings** → **When maximum wait time is reached, send caller to**. [RingCentral's guide](https://support.ringcentral.com/article-v2/10514-call-queue-set-up-call-handling-how-calls-transferred-group-members.html?brand=RingCentral\&product=RingEX\&language=en_US) | Queues cap at 25 callers and 25 minutes. Some plan tiers don't offer external forwarding |
| 8x8 (X Series) | Ring group or call queue → **Call forwarding rules** → forward to a telephone number. [8x8's guide](https://docs.8x8.com/8x8WebHelp/admin-console/Content/Set_up_Ring_Groups.htm) | Set it on the group — ring groups ignore members' own forwarding rules |
| Zoom Phone | Call queue → **Overflow** → route to a phone number. [Zoom's guide](https://support.zoom.com/hc/en/article?id=zm_kb\&sysparm_article=KB0065370) | Only works if the queue has a direct number of its own |
| Cisco Webex Calling | Hunt group or queue → **Call Forwarding** → **Always Forward Calls**, or **Overflow Settings** → **Transfer to phone number**. [Webex guide](https://help.webex.com/en-us/article/o6rfjeb/Manage-hunt-groups-in-Control-Hub) | Enter the number in E.164 form with a leading `+` |
| Dialpad | Department → **Business hours & call routing** → **Fallback Options**. [Dialpad's guide](https://help.dialpad.com/docs/set-call-routing-rules-for-departments) | Customer Care has to enable it, menus also need the [IVR external-number setting](https://help.dialpad.com/docs/ivr-external-number-company-setting), and US numbers only |
| Nextiva | Call group → **Forwarding** → **Call Forward When Unanswered**. [Nextiva's guide](https://help.nextiva.com/article/call-forwarding-overview) | Set it on the group — a member's own forwarding doesn't apply to distributed calls |
| Vonage Business Communications | Extension → **Call Forwarding** → **Forward All My Calls To**. [Vonage's guide](https://businesssupport.vonage.com/articles/answer/Call-Forwarding-24813) | Queues follow their extensions' forwarding, so edit the extension |
| GoTo Connect | Dial plan editor → the **External number** node with an **On timeout** branch. [GoTo's guide](https://support.goto.com/connect/help/what-do-the-dial-plan-nodes-do) | Turn on **Pass through caller ID**; an earlier **Modify caller ID** node overrides it |
| Intermedia Unite | Hunt group → **General** → **Timeout to** → **Phone Number**. [Intermedia's guide](https://support.intermedia.com/app/articles/detail/a_id/15235/~/managing-hunt-groups-on-intermedia-unite) | Keep the timeout short, or the far end's voicemail answers instead |
| Ooma Office | Add a **Shared External Line**, then choose it in an extension's **Call Handling**. [Ooma's guide](https://support.ooma.com/office/how-to-add-a-new-shared-external-line/) | Pro Plus plan, and one shared external line per account |
| Cytracom | **Phone Numbers → Call Forwards** to create the resource, then **Standard Routing** → **Forward** → **Route to**. [Cytracom's guide](https://help.cytracom.com/hc/en-us/articles/204726995-Forwarding-to-Outside-Lines) | Ring groups use their **After ringing group forward call** destination |
| Avaya Cloud Office | Call queue → **After Hours Call Handling** → **Unconditional Call Forwarding**. [Avaya's guide](https://support.avaya.com/kb/public/DOCS100558) | RingCentral underneath. Bring-your-own-carrier queues can't forward externally |
| Grasshopper | Extension → **Add a forwarding number**. [Grasshopper's guide](https://support.grasshopper.com/help/forward-incoming-calls-for-an-extension) | Never point a forward back at your own Grasshopper number |
| Google Voice | Not possible — ring groups can't forward to an external number. [Google's guide](https://knowledge.workspace.google.com/admin/voice/set-up-google-voice-ring-groups) | No license changes this. Publish a Thread number to clients directly instead |
## On-premises and self-hosted
| Phone system | Where to set it | Watch out for |
| --------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ----------------------------------------------------------------------------------------------------------------------- |
| 3CX | Ring group or queue → the **Destinations** for unanswered calls → an outside number. [3CX's guide](https://www.3cx.com/docs/manual/call-center-queues/) | Two hidden blockers catch almost everyone — [see below](#3cx-has-two-hidden-blockers) |
| Cisco Unified CM | Hunt pilot → **Queue Calls** → **Maximum Wait Time in Queue** → **Route the call to this destination**. [Cisco's guide](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/14SU2/cucm_b_feature-configuration-guide-for-cisco14su2/cucm_m_configure-call-queuing.html) | The calling search space must reach a route pattern for the number. **Queue Calls** disables **Forward Hunt No Answer** |
| FreePBX / Asterisk | Ring group → **Destination if no answer**. [FreePBX guide](https://sangomakb.atlassian.net/wiki/spaces/PG/pages/24314016) | That dropdown lists internal destinations only — add a **Misc Destination**. Set **Confirm Calls** to yes |
| Sangoma Switchvox | An IVR action of **Send to External Number**, then point the queue's **In Queue Call Routing** at that IVR. [Switchvox guide](https://sangomakb.atlassian.net/wiki/spaces/Switchvox/pages/447971342/How+Do+I+Setup+A+Call+Queue+That+Sends+Call+To+An+External+Number) | Queues can't dial out directly. The number needs an outgoing call rule set to **Allow** |
| Yeastar P-Series | Ring group or queue → the failover destination when nobody answers. [Yeastar's guide](https://help.yeastar.com/en/p-series-appliance-edition/administrator-guide/ring-group-overview.html) | Adding an external number as a *member* behaves differently from a failover destination |
| Grandstream UCM | **Basic Call Features → Ring Groups** → no-answer destination, or **Call Forward No Answer**. [Grandstream manual](https://documentation.grandstream.com/knowledge-base/ucm630x-series-user-manual/) | An external forward cuts the original ringing short — check your ring time |
| Mitel MiVoice Connect | Connect Director → **Features → Hunt Groups**. [Administration guide (PDF)](https://www.mitel.com/sites/default/files/s3_imports/Business%20Phone%20Systems/MiVoice%20Connect/MiVoice%20Connect%20Platform/19.3/en/3MiVoice%20Connect%20System%20Administration%20Guide.pdf) | Mitel publishes this as a PDF only |
| Altigen MaxCS | **Workgroup Configuration** → **Ring No Answer Details**. [Administration manual (PDF)](https://altigen-support.com/wp-content/uploads/2022/05/ACM-Administration-Manual-1-1.pdf) | PDF-only documentation |
## Contact center platforms
| Platform | Where to set it | Watch out for |
| ------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ----------------------------------------------------------------------------------------------------------- |
| Genesys Cloud | Architect flow → **Transfer to Number**, with **Connect Timeout** and a **Failure** path. [Genesys guide](https://help.genesys.cloud/articles/transfer-to-number-action/) | E.164 only — Genesys warns that other formats cause carrier errors |
| Five9 | IVR script → **Third Party Transfer Module** → **Third Party Number**. [Five9 guide](https://documentation.five9.com/bundle/ivr-admin/page/ivr-admin/modules/third-party-transfer-module.htm) | Format depends on whether your domain is E.164-enabled; otherwise 10 digits, no leading `1`, no punctuation |
## Platform-specific blockers worth knowing
### Microsoft Teams needs Pay-As-You-Go
Since **1 November 2025**, a Calling Plan license alone no longer lets an auto attendant or call queue transfer a call to an external number. The resource account needs funded Pay-As-You-Go or Communication Credits, or the redirect fails silently. Full steps are in [Enable Teams Pay-As-You-Go calling for resource accounts](/ai-agents/microsoft-teams-pay-as-you-go-resource-account-calling).
Two more Teams-specific points:
* **"We're on Teams" isn't a complete answer.** Whether the PSTN side is a Calling Plan, Operator Connect or Direct Routing changes what's required, and Microsoft doesn't support transfers *between* those trunk types. Establish which one you have before troubleshooting.
* **Operator Connect tenants** may need their carrier to permit these calls, so loop the carrier in if a redirect fails despite correct licensing.
### 3CX has two hidden blockers
Both are common enough that they're the first things to check, and the symptom is misleading — the log shows `NO ANSWER` as if the far end never picked up:
* The global option **Allow forwarding to external numbers in Ring Groups and Queues** has to be enabled.
* The forwarded leg originates from the **system**, not from an extension, so an outbound rule scoped to *calls from extension* or an extension group never matches. Build the rule on destination criteria — prefix or number length — instead.
Enter the number in whatever format your trunk expects (`+1…`, `1…` or the 10-digit form). Punctuation such as `813-555-1212` fails.
If you're also using a SIP trunk with Thread, see [SIP trunks and caller ID](/ai-agents/voice-ai-sip-trunks-and-caller-id) — 3CX rejects calls to DIDs it doesn't recognize, which affects trunk testing.
### 3CX counts a forwarded call as two active calls
By default, a call forwarded from 3CX to Voice AI keeps the original inbound leg active in 3CX until a technician answers the callback from Voice AI. Both legs show as active on the **Panel** view during that window, so every Voice AI call consumes two of the concurrent-call slots on your 3CX plan. On plans with a low concurrent-call cap (for example the 8-call tier), this can push you over the limit as soon as a few calls roll to overflow at once.
Switch the forward to use **SIP 302 call deflection** to avoid this. With deflection, 3CX hands the caller off at the SIP layer and releases the inbound leg immediately. Only the callback leg from Voice AI counts against your concurrent-call cap once a technician picks up.
Enable it on the ring group or queue's **Destinations** — set **Forward external calls to** to **External Number**, enter the Thread **Attendant** or **Overflow** number, and check **Use Call Deflection (302)**.
Two things to confirm before you rely on this:
* Your SIP carrier has to accept 302 redirects. Some carriers, including Twilio, block them by default — if calls stop connecting after you enable deflection, your carrier is likely the reason.
* After the change, place a test call and watch the **Panel** view. The forwarded call should disappear from the panel as soon as 3CX hands it off, then reappear as a single active call when Voice AI calls back and a technician answers.
## If your phone system isn't listed by name
Some phone systems are delivered under a provider's or an MSP's own brand. The admin console still comes from one of a handful of platforms, so one of these sets of documentation will match what you're looking at.
| If your phone system is… | Documentation that matches |
| ------------------------------------------------------------------------------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| SkySwitch, Crexendo, Viirtue, Reinvent Telecom MyCloud, or a cloud PBX under your own brand | [Configure call queues (ACD)](https://docs.skyswitch.com/en/articles/83-how-to-configure-call-queues-acd) — **Forward if unavailable** and **Forward if unanswered**. [Crexendo's guide](https://www.crexendo.help/en_US/the-crexendo-guidebook-for-managers/crexendo-guidebook-for-managers-how-to-create-and-edit-call-queues) covers the same fields. Keep the agent ring timeout below the queue ring timeout, or the queue's exit never fires |
| bvoip or 1stream, or a hosted PBX billed per extension with a browser-based client | The [3CX](#3cx-has-two-hidden-blockers) notes below. bvoip's [call flow](https://docs.1stream.com/en_US/551328-call-flow/what-is-a-call-flow) article covers the concepts but not external forwarding, so confirm the specifics with bvoip |
| Comcast Business VoiceEdge, Cox Business, Spectrum, or a regional telco's hosted voice | Ask your carrier for the *call forward not answer* or *no answer transfer* feature on the hunt group. It is often provisioned per seat rather than self-service |
| Avaya Cloud Office, AT\&T Office\@Hand, or TELUS Business Connect | The RingCentral wait settings above |
**Some platforms publish nothing you can read.** NetSapiens, CoreDial and CoreNexa, Star2Star, Evolve IP, RingLogix and Mitel MiVoice Business keep their admin documentation behind a partner or customer login. Ask your provider where the queue's no-answer destination is set — and on Mitel MiVoice Business, also ask about the class-of-service permission and route that allow an external forward at all.
## Find the rule yourself
Not finding your platform above isn't a dead end — the pattern holds everywhere. Open the call queue, ring group or hunt group your support calls land in, find the rule for the condition (*no answer*, *no agents available*, *maximum wait time*, *timeout*, *overflow*, or your *after-hours* schedule), and set its destination to an external number — your Thread **Overflow** number. To have Voice AI answer first instead, point your support number at the **Attendant** number.
If every destination option is internal — extensions and voicemail only — external forwarding is disabled or unlicensed on your platform, which is a question for your phone system provider rather than for Thread.
[Forward your phone system to Voice AI](/ai-agents/connect-your-phone-system-to-voice-ai#make-the-forward-in-your-phone-system) has the full list of words vendors use for both, and the checks to run before you go live.
Still stuck, or on a platform you'd like added here? Contact Thread support at [help.getthread.com](https://help.getthread.com).
## Next
Which Thread number goes where, mapped to how your call flow is set up today.
What to check when calls don't arrive, transfers fail, or tickets don't appear.
## Related topics
- [Forward your phone system to Voice AI](/ai-agents/connect-your-phone-system-to-voice-ai.md)
- [Replace your phone menu with the Auto-Attendant](/ai-agents/voice-ai-setup-phase-3-the-auto-attendant-walk-run.md)
- [Troubleshoot Voice AI](/ai-agents/voice-ai-troubleshooting.md)