Vodafone Mobile Connect Card Driver for Linux makes it easy to get connected with any of the GPRS/3G cards supported. Besides managing connections with different technologies like GPRS, UMTS, and HSDPA, this applications supports receiving and sending SMS, access to contacts, and offers diagnostics information for troubleshooting.
Divmod Sine is a standards-based voice-over-IP application server, built as an offering for the Mantissa application server platform. It owes much of its development to the Shtoom project, which implements a soft-phone in Python. Sine provides a SIP registrar, SIP proxy, third party call control, voicemail, and configuration through the Web based on Divmod Mantissa.
pyWebSMS is a program which lets you send SMS through the Internet without opening a Web browser. You can send multiple SMS, save your contacts, view the history, and much more. It's completely modular, so you can add or remove providers for sending SMS. You can make your own module for your provider if one doesn't exists yet by programming it in Python.