Kannel : (Free)
Kannel is an open source WAP and SMS gateway.
SMS, short message services, are widely used all over the world in huge amounts. The main use for Kannel is to link HTTP based services to various SMS centers using obscure protocols.
WAP, short for Wireless Application Protocol, is a collection of languages and tools and an infrastructure for implementing services for mobile phones. Traditionally such services have worked via normal phone calls or short textual messages (e.g., SMS messages in GSM networks). Neither are very efficient to use, nor very user friendly. WAP makes it possible to implement services similar to the World Wide Web.