The Alamin GSM SMS Gateway is a group of daemons that allows you to send/receive SMS messages from any GSM device that supports AT+ commands (GSM modems or GSM mobile phones) or supported by Gnokii. A client program allows you to send messages from any IP client. An SMTP interface is provided to allow MTAs to send SMS directly to the GSM network. IMP (Incoming Message Processor) modules allows you to extend functionality to implement banking, network administration, bd querys, etc. from a GSM mobile phone.
Bayonne is the telephony server of the GNU project. It offers a script-driven threaded multi-line state event telephony service on GNU/Linux, xBSD, and Microsoft Windows for building voice response systems, and uses telephony plugins for runtime driver configuration. It also features "TGI" for making Perl applications "telephony aware". It may be used to build telephony-based system administration, home automation, automated attendant, v-commerce, and voice messaging systems.
El Cid is a caller ID program for Linux. It just sits on your modem waiting for something to happen, parses the input, and displays the caller ID information. All records are logged to a file in csv format so you can easily parse it for logging into a database, viewing on the Web via CGI, etc.
mptc is a Perl script to help you work out whether you're on the cheapest mobile phone network/tariff for your phoning habits. You feed it an itemised phone bill and tariff pricing information, and it will tell you how much that bill would have cost on different tariffs. So far it only supports UK network pricing systems, but could easily be extended and applied in other countries.
sms-queue handles an SMS queue for small networks or single user machines. It is designed for areas where many SMS messages are sent. It does not actually send the SMS itself, but instead calls an external application (depending on the SMS gateway you want to use) via a simple standard interface. The communication between client and server is based on a simple ASCII protocol over TCP/IP which should make it easy to develop your own frontend.
Bluel VMail is a semi-complete voicemail system that supports automated attendant, call transfer, e-mail delivery of voicemail messages, etc. It was designed to work with the Diamond SupraExpress ISA modem and Panasonic KX-T61610 hybrid phone switch (cheap!), but is probably portable to similar configurations.