AI voice integration

Phone numbers for Synthflow — SIP trunk setup with DIDHub

Synthflow voice agents work cleanly with DIDHub via BYOC SIP. Per-DID assignment to specific Synthflow assistants, outbound from Synthflow campaigns with proper Caller-ID and STIR/SHAKEN.

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Why DIDHub for Synthflow

STIR/SHAKEN A-attestation. For US outbound, A-attestation is a hard requirement to avoid mobile carrier spam labeling.
Per-DID flat pricing. Predictable per-Synthflow-customer DID economics.
136 countries. Global Synthflow deployments without juggling multiple carrier vendors.
Bulk provisioning API. Scale from 1 DID to 10,000 with the same flat per-DID rate.

BYOC setup — step by step

Sign up at /signup and provision DIDs.
Generate DIDHub SIP credentials.
In Synthflow: open BYOC / SIP trunk settings.
Paste DIDHub credentials.
Bind DIDs to Synthflow assistants.
Test inbound + outbound.

Documentation note. Synthflow's BYOC / SIP trunk configuration UI changes occasionally. The steps above reflect the current pattern at time of writing. If a screen has moved, the underlying values (SIP URI, credentials, allowed source IPs) are the same — check Synthflow's docs for the latest UI path.

Caller-ID configuration

Set the DIDHub DID as outbound Caller-ID in your Synthflow assistant config. DIDHub validates and signs with A-attestation.

For US/CA outbound: DIDHub signs every call with STIR/SHAKEN attestation A on DIDHub-allocated and DIDHub-ported numbers. This is the level that mobile carriers (T-Mobile, Verizon, AT&T) treat with baseline trust — calls signed with weaker attestation are increasingly flagged as “Spam Likely” or sent straight to voicemail. See STIR/SHAKEN explained for the full background.

For non-US destinations: present a local DID as Caller-ID for best answer rates. AI agent calling a Madrid customer should present a +34 (Spanish) Caller-ID, not a US number. DIDHub serves 136 countries with dedicated landing pages so you can match Caller-ID to destination.

Latency & regional ingress

Realtime AI voice is brittle to network latency — an extra 100ms of SIP egress can break the natural-conversation feel. DIDHub operates SIP/RTP edges in:

NOAM: Ashburn (US-East), San Jose (US-West), Dallas
EU: Frankfurt, Amsterdam
APAC: Singapore, Tokyo
MENA: Dubai

Pick the edge nearest to your Synthflow inference region. Typical sub-50ms regional ingress for the closest pair. If you need a region we don't list, talk to [email protected] — we add edges in response to customer demand.

FAQ

Does Synthflow support BYOC?

Yes. The exact configuration path depends on Synthflow's current UI version.

Can I port Synthflow-bundled DIDs?

Generally yes via standard LNP. Coordinate with Synthflow's support.

Does Synthflow handle international DIDs?

Yes via BYOC. The Caller-ID just needs to be a valid DIDHub-allocated DID.

How do I scale Synthflow + DIDHub for high volume?

Allocate a DID pool and rotate via Synthflow's outbound config. DIDHub's bulk API supports it.

Provision your first Synthflow DID

Sign up at /signup, pick a country / area code, and route the DID to your Synthflow BYOC SIP trunk. $1.99/mo for a US number, sub-60-second activation on most countries. No commits.

Ready to get a number?

Pick a DID in 130+ countries from $1.99/month. Activates instantly on most numbers.

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