SMS spoof is a PalmOS application that allows you to send spoofed SMS messages. It uses a dialup connection to an EMI/UCP-compatible SMSC. It can be used with a modem connected to the Palm, such as an IR link to a GSM phone with a built-in modem. SMS spoof has been tested with Telenor's SMSC in Norway, but it should work with any SMSC that supports the EMI/UCP protocol, as long as no authentication is required.
YaPS (Yet anothewr Paging Software) is primarily designed to send message to pager devices (including cellular phones) which are able to receive SMS. It is a simple command-line driven program with a global and a personal configuration file, but the protocol implementation is kept as a seperate library. YAPS can transfer Pager Messages with UCP, TAP, and Script Protocol.
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.
PreViking is a telephony daemon written in C. It has been designed with a modular structure that easily allows the addition of different services and the support of different hardware. Current services include a calling card service and a call- back service. PreViking provides an API which includes many functions to do different telephony operations such as call switching, playing/recording messages, and listening/playing DTMF.