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A saved hostname proves only that an endpoint was entered. It does not prove direction, authentication, source addresses, or a successful inbound call. Keep the exact DID, route it to the platform SIP FQDN, and obtain current provider-to-destination authentication details. If no stable list is published, ask support for the account’s complete SIP-signaling source CIDRs and failover regions. Never use media ranges or another customer’s addresses. Running your own PBX or contact-center platform — 3CX, Asterisk/FreePBX, Starface, Genesys Cloud, Five9, or Aircall? See PBX & contact center platforms for step-by-step setup, codec settings, and the failure modes specific to each.
If a provider doesn’t support a static SIP trunk at all, you don’t have to give up on the number. Forward it to a number purchased through the platform for inbound calls, and place outbound calls from that platform number instead.
Status: sip.1und1.de is normally a registrar/termination host, not evidence of external FQDN forwarding. No verified global source list is included. Action: confirm product support, sent DID format, and all signaling sources with 1&1.
Status: Fonial documents SIP users and trunking, but SIP-URI forwarding is account-dependent. sip.plusnet.de is an outbound host, not an inbound allowlist. SIP trunking with the platform requires Fonial’s paid PLUS plan — the free tier can’t be used this way. Action: configure outbound separately and obtain current forwarding/source details from Fonial. Expect the SIP user to show Offline in Fonial’s dashboard permanently; that’s expected, since the platform never sends a SIP REGISTER, not a sign the integration is broken.
Status: a localphone.com endpoint alone is not a verified inbound profile. Action: confirm external SIP-URI routing, DID format, transport, and signaling sources with Localphone.
Status: the hostname can identify a PBX or reseller; no global list is verified. Action: identify the actual operator and obtain account-specific public signaling addresses.
Status: routing a DID to a SIP URI is supported, but auth and sources follow current account/trunk documentation. DIDWW uses two separate trunks — inbound routes to the platform SIP FQDN, and outbound authenticates against out.didww.com. Action: use current DIDWW sources; never reuse DIDLogic addresses. Send outbound numbers in E.164 without the leading + — DIDWW expects that exact format, and it’s an easy detail to miss.
Status: credentials and routing are account-specific; no global list is verified here. Zadarma offers two integration paths — a PBX extension, or a direct SIP connection with External Services → SIP URI enabled per number. Action: confirm FQDN forwarding plus documented downstream Digest or current signaling CIDRs. Either way, check Zadarma’s Voice Geographic Permissions: international outbound dialing is blocked by default per destination country, and a call to an unlisted country fails silently rather than with an obvious error.
Status: capabilities vary by product and region. sipcall’s default trunk type registers (Endgerät); the platform needs the non-registering, static Anlagenanschluss mode instead — not the option a new sipcall customer would normally pick. Action: ask support for external SIP-URI routing, number format, transport, and current sources. Use Digest authentication, and set codecs to G.711 a-law with Opus and G.722 disabled (the Swiss default). If outbound calls get a 403, check that the caller ID is verified on the account.
Status: generic SIP/BYOC depends on the purchased product. RingCentral has no wholesale SIP trunk for retail accounts; connect by provisioning a Generic SIP IP Phone instead, which requires MVP/RingEX Standard or higher — entry plans don’t expose it. Action: confirm external SIP destination support and request current regional signaling ranges. Always point at the global sip.ringcentral.com host, never a regional sipXX.ringcentral.com address (those are reserved for RingCentral’s own desk phones). A newly created SIP endpoint needs one to two minutes to propagate through RingCentral’s anti-flood protection — testing immediately produces spurious 403/404 errors, and retrying during that window can extend the lockout.
Status: Voice Connectors use region-specific signaling information. Chime’s Voice Connector defaults to Encryption: Enabled, which requires TLS and SRTP — if the platform side of the trunk falls back to plain UDP on port 5060, the call fails with no media and no obvious error. Action: use the current data for the selected AWS region; never reuse another region’s addresses. The outbound host follows <voice-connector-id>.voiceconnector.chime.aws. Chime also gates outbound by Calling Plan — a destination country not explicitly enabled on the AWS account is blocked, independent of any platform-side dialing permissions.
Status: no verified direct external-FQDN profile is documented here. Action: treat it as unsupported until Placetel confirms route, number format, auth, transport, and source ranges in writing. No static trunk? Use the fallback above.
Status: capabilities and SBC addresses vary by country/product. Action: request the exact external SIP route and regional source networks for the account. No static trunk? Use the fallback above.
Status: Cloud PBX interconnect is product-controlled; no global list is asserted. Action: use a support-assisted setup and only the destination/source networks supplied by NFON. No static trunk? Use the fallback above.
Status: trunking and forwarding are product-specific; no global list is asserted. Action: confirm external SIP-URI routing and current signaling sources before saving. No static trunk? Use the fallback above.
Status: no current provider-to-platform authentication profile is documented here. Action: identify the exact product and region, then obtain the current FQDN-routing method and complete signaling sources from the provider or account portal.
Status: a saved hostname or credential mode is not proof of downstream Digest support. Action: confirm the account’s external SIP destination support, DID format, transport, and current public signaling sources.

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Required confirmation

Ask whether the DID can be delivered to an external FQDN without REGISTER; the exact DID format in the Request-URI; whether the provider authenticates toward the destination with Digest and where those origination credentials are set; otherwise all signaling CIDRs and failover regions; TCP 5060 or TLS 5061; and whether SRTP is required. Only an external call with a platform inbound record, the assigned assistant, and two-way audio confirms the integration. Reject allowlist entries that contain prose, placeholders, hostnames, or unrelated public resolvers such as 8.8.8.8. A provider network written without its CIDR prefix is only one host and must not be silently expanded or corrected. Sources: DIDWW, Fonial, Amazon Chime, Zadarma, sipcall, RingCentral, Placetel, Peoplefone, NFON, Sipgate. Accessed 22 August 2026.