Phone is a telephony application, providing a user interface aiming at the implementation of a full-featured smartphone. It can also be used to handle GSM modems in a desktop environment.
It is available under the GPL version 3.

It supports multiple telephony backends, of which:

• Hayes/3GPP (AT commands on serial lines)
• Sofia-SIP (VoIP, experimental)
• Purple (XMPP and more, experimental)

It can also be extended with additional plug-ins, like:

• dialing GPRS/3G connections
• parental control
• profile management
• integration with DeforaOS Panel
• support for USSD codes
• improved hardware support (Openmoko Freerunner, Nokia N900...)

Wiki page:
https://www.defora.org/os/wiki/3489/Phone