SMPP is strictly for SMS, and you need a direct connect to the network's
SMSC to use it.

This sudden interest in SMPP is puzzling. Several times over the life of
FreeSwitch I've offered to resurrect a SMPP platform that was heavily
used about 12 to 15 years ago, and make it open source. That platform
has SGIP and a couple of other protocols, too. I've never had enough
positive response to make me go ahead with the work.

Nice, if you have it why not just put the code on github (or elsewhere) and let the community take care of integrating it/fixing it to work with FreeSWITCH? (Assuming you don't have the time/interest on doing it).

Nothing peaks the interest as a little of code browsing :)