The AT Emulator can emulate a communication device, like a modem. The AT interface can be accessed through the console, a TCP or telnet connection or a virtual COM port.
Theis is the public source code, which is written in Java. Feel free to modify and use it for any commercial and non-commercial purposes. Feel free to share and redistribute this software as long as you give credit to Victor Celer.
A precompiled package and some usage examples can be found here: https://www.celersms.com/at-emulator.htm