TEL

"tel:" URIs are used to bridge the gap between VoIP and PSTN. A SIP client might use a "tel:" URI to initiate a PSTN connection. Commonly the call is routed via a PSTN gateway like Asterisk PBX or a SIP provider.
The URIs are often used in conjunction with ENUM.

• Tel URI's that begin with a "+" is an E.164 phone number
• Tel URI's can also be local, only working within a limited context - like your office or your country
• Tel URI's are not dial strings for modems

See also

• RFC 3966: The tel URI for Telephone Numbers
• RFC 4694: Number Portability Parameters for the "tel" URI
• Asterisk
• ENUM
• SIP URI: The SIP URI