Phone system forwarding directory

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 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.

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Cloud phone systems

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On-premises and self-hosted

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Contact center platforms

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Platform-specific blockers worth knowing

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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. 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.

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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 — 3CX rejects calls to DIDs it doesn’t recognize, which affects trunk testing.

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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.

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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. 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.

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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 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.

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