Setting a FlyNumber to VoIP means its incoming calls go straight to a SIP address you own (SIP is the standard that VoIP apps, PBXs and desk phones use). That can be your own PBX, a hosted VoIP provider, a softphone service or an AI voice platform. There's no per-minute charge on incoming calls: unlimited incoming minutes*.

In your panel, open the number, and in the Call Handling card pick Forward to SIP / VoIP Address. You can do the same while ordering a number. The form has four fields: Transport, Host, Port and Username. Only Transport and Host are required. Save, and the change takes effect right away.

Each field is explained below. For the full walkthrough, including examples for VAPI, LiveKit and other AI platforms, see Set to VoIP in our docs.

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Transport

  • The first thing we ask is how the call should travel to your server. The protocol is always SIP; Transport decides whether that SIP traffic is encrypted.
  • UDP is the default. It's the fastest path and works with almost every SIP server and softphone. Signaling and audio travel unencrypted.
  • TLS encrypts the leg between FlyNumber and your endpoint: signaling over TLS 1.2/1.3 and audio with SRTP. Your server must support SRTP (SDES), or the call won't connect.
  • Pick TLS when you actually need the encryption, otherwise UDP is fine. Some AI platforms, like ElevenLabs, require TLS. See what TLS does and doesn't cover.
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Host

  • Next we ask for a Host: your SIP server's hostname or IP address.
  • When using a hosted VoIP provider this is the part after the @ in your SIP address. If your SIP address is john@sip.acme.com, the host is sip.acme.com.
  • If you're not sure what your SIP address is, contact your provider or search their documentation for "SIP settings".
  • When pointing a FlyNumber at your own PBX (Asterisk, FreePBX, 3CX, FreeSWITCH) this is the public IP address or hostname of that server. If your Asterisk box is reachable at 12.34.45.7, that's what you enter.
  • Domains, IPv4 addresses and bracketed IPv6 addresses like [2001:db8::1] are all accepted. Single-label names such as localhost are rejected.
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Port

  • Port is optional, and in most cases you should leave it blank.
  • With Port blank, we route the call using the DNS records your SIP destination publishes. That's exactly what hosted services like sip2sip.info, Twilio, voip.ms and most modern providers expect.
  • Typing the standard ports, 5060 for UDP or 5061 for TLS, is treated the same as leaving it blank.
  • Only enter a port if your own PBX listens on a non-standard one, say 6060. That overrides DNS and connects directly to that port on the host.
  • The most common setup mistake is a hosted provider's domain with a non-standard port. Calls then fail almost instantly, because the domain's public IP doesn't answer SIP. Clear the port and try again.

Username

  • And finally the Username, also called the user or extension. It's the part before the @ in the SIP address we send the call to.
  • It's optional. Leave it blank and we use your FlyNumber as the username.
  • With a hosted VoIP provider, enter your account username there. If your SIP address is john@sip.acme.com, the username is john.
  • On a PBX, enter the extension the call should ring. If Asterisk or FreePBX has extension 101 for a particular phone or user, enter 101 and incoming FlyNumber calls land on that endpoint.
  • AI voice platforms like VAPI and LiveKit expect your FlyNumber in international format, for example +13025551234. See the AI platform examples.
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Allow our server, then test

  • Forwarded calls, both signaling and audio, come from one FlyNumber server: sip.flynumber.com at 138.197.42.26. If your PBX or platform filters by source IP (an ACL, "allowed addresses" list or firewall rule), allow that address first. Otherwise calls may ring but never connect. Codecs, RTP ports and DTMF details are on our IP addresses page and in the docs' technical specifications.
  • Make a test call after every change. If something's off, your call logs show a status that points to the cause, and the docs have a troubleshooting table for each one.
  • Quick tip: set Host to iptel.org and Username to music to test your FlyNumber before your own server is ready. You'll hear music when you call the number.

Need to log in with credentials? Use FlyNumber SIP

Set to VoIP pushes calls out to your server anonymously, so it can't sign in to a provider or platform that requires a registered, password-protected SIP connection. The cleaner fix is to flip the relationship: switch Call Handling to FlyNumber SIP, and your device registers to us instead.

FlyNumber SIP gives you your own SIP credentials. Plug them into any softphone, desk phone or PBX and your FlyNumber rings there, on up to 5 devices. Outgoing calls show your FlyNumber as the caller ID and are billed per minute from your prepaid balance at our calling rates. Incoming calls are included with the number's monthly rate.

Voicemail and encrypted calls (TLS + SRTP) are built in, with no setup fee and no monthly fee for FlyNumber SIP itself. No SIP server to expose, no IP list to maintain. Some number types restrict outbound calling due to local regulations.

Set up FlyNumber SIP
Incoming call Rings every registered device
🇺🇸
+1 307 429 0155 United States · Sheridan, WY
Included in the number's monthly rate
Outgoing call Dial out from any SIP app or desk phone
Caller ID +1 307 429 0155
🇺🇸 Your number
Billed per minute from your prepaid balance
FlyNumber SIP Make and receive calls
Built-in VoIP
Your own SIP credentials — works with any SIP app or desk phone.
Username13074290155
Password••••••••••
SIP serversip.flynumber.com
DevicesUp to 5
Phone, desktop and desk phone ring together
VoicemailBuilt in
Picks up when no device answers

The other ways to handle your calls

Watercolor illustration of a desktop computer, server, smartphone, tablet and laptop, the kinds of devices you can register with FlyNumber SIP.
FlyNumber SIP
Your own SIP credentials from FlyNumber (SIP is the standard that VoIP apps and desk phones use). Register any SIP app, desk phone or PBX, up to 5 devices, and make and receive calls, with voicemail built in. Incoming calls are included with your number's monthly rate; outgoing calls are billed per minute from your prepaid balance. Set up FlyNumber SIP.
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Forward to a Phone Number
Send calls to any mobile or landline, anywhere in the world, at a low per-minute rate from your prepaid balance. How forwarding works.
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Forward to SIP / VoIP Address
Already use a VoIP provider, PBX, softphone service or AI voice platform? Point your FlyNumber at its SIP address and calls arrive there with no per-minute charges on incoming calls: unlimited incoming minutes*. Set your FlyNumber to VoIP, connect an AI voice platform like VAPI or ElevenLabs, or see how it works with any VoIP solution.
Cloud connected to various devices including a server, laptop, smartphone, and desktop monitor.
Cloud Phone System (optional)
Need a voice menu, ring groups, queues, business hours or call recording? Add our cloud phone system for $14.95/month flat, one price for your whole account, with up to 30 users. Usually you don't need it: see when it's worth adding.

Note

Switch between them any time in your panel. A fifth option, Park the Number, stops the number ringing anywhere (callers hear busy) with no call charges.

Every option is included with a virtual phone number from any of the 90 countries on our coverage page. See pricing for monthly rates and the Rates page for per-minute calling.

Get your number

*Unlimited incoming does not apply to toll-free or metered numbers.