The OpenSmpp API is an open source Java library implementing the SMPP (Short Message Peer to Peer) protocol. It is based on the original Logica OpenSMPP API.
At the moment only SMPP version 3.4 is supported.
Support for SMPP used to be provided via the forums at smsforum.net (no longer in existence); but since SMS Forum ceased operations at the end of 2007, official support is no longer available.