E.164 International Phone Number Formatter, SIP Trunk & Virtual Number Cost Calculator (2026)

ITU-T Recommendation E.164 defines the global public telecommunication numbering plan. A valid E.164 number begins with a `+` sign, followed by a 1-to-3 digit Country Calling Code (e.g., `1` for NANP US/Canada, `44` for UK, `91` for India), followed by the National Destination Code (area/carrier code) and Subscriber Number—containing **at most 15 digits total** and zero spaces, dashes, or parentheses (`+14155552671`).

In many countries outside North America, dialing `0` before the area or mobile code is a domestic **Trunk Prefix** that signals the local telephone exchange to route a national call (for example, `020 7946 0921` in London or `0412 345 678` in Australia). When dialing internationally or formatting to E.164, the country code (`+44` or `+61`) replaces the trunk prefix, yielding `+442079460921` and `+61412345678`.

Strict E.164 (`+14155552671`) only identifies the public PSTN subscriber line and cannot contain extensions. To include an extension in web links or SIP signaling, use **RFC 3966** syntax: `tel:+1-415-555-2671;ext=104` or append DTMF pause commas (`+14155552671,,104`) on mobile dialers.

Consumer and SMB virtual calling apps bundle PBX hosting and charge a flat $15–$30 per user seat per month regardless of call volume. Wholesale SIP trunk providers (like Telnyx, Twilio Elastic SIP, or Bandwidth) decouple phone numbers ($0.80–$1.50/month per DID) from metered usage ($0.003–$0.008/minute), allowing 20 agents to share a pool of concurrent channels at a fraction of per-seat pricing.

Application-to-Person 10-Digit Long Code (A2P 10DLC) is a mandatory registration system enforced by US mobile carriers (AT&T, T-Mobile, Verizon) for any business sending SMS from virtual numbers. In addition to the base SMS segment rate (~$0.0079), carriers charge a one-time Brand/Campaign registration fee plus a ~$0.003 per-segment carrier pass-through surcharge.