Qtopia (former Qt Palmtop Environment) is a platform for linux-based PDAs, Webpads and mobile-phones developed by Trolltech. License As most Trolltech products Qtopia is dual licensed under the free License:GPL or closed-source which requires a licensing fee then.

Twinkle is a software phone for voice over IP communications using the SIP protocol. You can use it for direct IP phone to IP phone communication, or in a network using a SIP proxy to route your calls.

WengoPhone is a multi-platform VOIP client sponsored and developed by Wengo and MBDSYS. The GUI part is Qt based, and the VOiP and Video-over-IP engine is based on the eXosip, oSIP, oRTP, and ffmpeg projects.

Gammu (formerly known as MyGnokii2) is a cellular manager for various mobile phones/modems.