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.
SMSLink implements a client/server gateway to the SMS protocol (short messages on the mobile phones). It requires the use of dedicated hardware (a serial GSM module). Both SMS emission and reception are supported, either in text-mode or in PDU-mode. It also includes an SMS to eMail gateway module. The server runs under Linux and FreeBSD and supports interactive mode via telnet. The command-line client already exists for Linux, FreeBSD, Solaris, HP-UX, and Win32. A basic Web interface is also provided.
VOCP is a complete messaging solution for voice modems, with voicemail, fax, email pager, DTMF command shell and Text-to-Speech support, 4 graphical interfaces, and a Web interface. Callers navigate the system using a touch-tone phone and may send and receive faxes, voice mail, and pager messages, listen to text/HTML email messages, or execute configured programs on the host and hear the resulting output.
Linphone is an audio and video Internet phone with GTK+ and console interfaces. It uses the SIP protocol, and is compatible with most SIP clients and gateways. It can use various audio and video codecs such as Speex, GSM, G711, G722, ilbc, amr, Theora, H263-1998, MPEG4, H264, VP8, and snow.