I've modified the smsc_smpp module to behave as smpp server. Modifications were done on CVS dated about 2 weeks ago. At the moment it seems to work smooth, but probably more features should be added, also I believe there're memory leaks. Authentication done using mysql database. At the moment it simply allows users to connect with SMPP gateway and send messages thru, after receiving the message from smpp, it matches user/pass from DB and resends the sms with Kannel HTTP query to the gateway. Middle layer can serve as billing system as well. To simplify the whole thing, the smsbox is not being used.
The original Kannel functionality is kept, while the smsc driver is called "smpp2", and can be activated from config file if needed. Is there any interest on adding this to Kannel CVS ? P.S. at the moment we supply this solution to some of our customers, but I'm willing to share the source so someone can help me in bugtracing :)