Gammu is a cellular manager for mobile phones/modems. It contains libraries and functions for ringtones,logos,phonebook,SMS,etc. (used by external software), a command line version (with backup/restore) and SMS gateway (with MySQL and PostgreSQL supp
JSMS-Gateway is an embeddable/standalone smsgateway to enable applications to easily leverage
SMS within their application[s] and/or provide solutions using SMS.
LemonSMS is a java library that enables developers to integrate sending of SMS messages using a GSM modem or compatible phone. The library is integrated into Aubey(http://www.sf.net/projects/aubrey) which has a mini SMS gateway implementation.