python-gammu is a set of Python bindings for Gammu, the GSM mobile manager for various cellular phones. It can work with any phone that Gammu supports, including many models by Nokia, Siemens, and Alcatel. python-gammu is now part of the Gammu project and it does not have separate releases anymore.
reSIProcate is a high performance, object-oriented, C++ sip stack that is compliant with RFC 3261. It includes support for a wide variety of operating systems, including Windows and Linux. It has full support for UDP, TCP, and TLS transports on both IPv4 and IPv6. It also implements the full set of specifications for DNS usage in SIP, including NAPTR and SRV lookups (RFCs: 3263, 2915, 2782) using an asynchronous DNS library (ares).
sYnergy is a Web-based groupware and communication solution for use with an intranet. It includes email mailboxes, a fax viewer and sending function, contact lists, an appointment and task management function, a picture database, and a function for listening to voice messages. The extensive user management enables administrators to assign various permissions to each user and to exchange data e.g. contacts, appointments, or tasks. It also offers a function to import existing data.
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.