Below is a listing of open source software having to do with Telephony. For a list of VoIP and business telephone providers please visit Voip-Info.org.
Uranium, is a program which communicates with any commnunication device (such as a Modem) that is plugged in a serial or usb device. It can change the device settings, receive and make calls, receive and send faxes and it is an answering machine too
The TrainPlanner is a program to find public transport routes with you mobile phone. The plans the application uses have to be added to the MIDLet. To do that there is a J2SE Application where you can create Plans and finaly bundle them to the Midlet.
Free Open Source ISDN BRI Caller ID Program for netMod ISDN Terminal Adapter