Today I ported my Python SMPP client library to PHP, I had to redesign the whole library because the old design was very bad, and with the new design it became very small, and trivial library.

Most of my work was on a library to convert between window-1256 charset used by most Arabic computers, to UTF-16 (big endian) used by GSM phones.

The new SMPP library supports long and flash messages, you can try it from SAUDI NET Portal.

update: You can download the library from:
SMPP PHP Client