As the name imply, OpenSMPP is an open source SMPP API that written in Java. It is conform to SMPP 3.4 while SMPP 5.0 is in the road map.
It is originate from Logica Open SMPP until version 1.3. And was continue to be maintain in sourceforge. So you may found version 1.3.7 at OpenSMPP with some important bugs fixed. It is release for exisiting code that tie to Logica Open SMPP package namespace.
This API is handy for development of ESME that bind to SMSC. All PDU required to interact with SMSC is provided. Receiving PDU is by implements your own listener which make you code clean from thread and infinite loop.
It will really be better if there is something similar to ExceptionListener in JMS for developer to capture connection failure.