SMSID provides a Linux PAM that allows the use of a GSM cellular phone with SMS capabilities as a hardware token in a strong authentication system.
In addition to the Linux PAM module, an extensible SMS server is included. This server is written in Java.
The server currently supports the Falcom A2D GSM modem but the server is designed to allow other GSM devices to be supported with a minimum of effort.
Take the SMS Device Survey
For more information see the SMSID Project Page at sourceforge.net