Mbuni - Provides an open source MMS gateway module for Kannel. - http://www.mbuni.org/
Hellkvist - Produces Mmslib which is a PHP library for encoding and decoding MMS. - http://www.hellkvist.org/software/
Openwave Developer Network - Tools & SDK - MMSC - Describes how to access its MMSC server for testing end-to-end delivery of MMS messages. - http://developer.openwave.com/dvl/tools_and_sdk/test_servers/mmsc/
NowSMS Forum - Although this is a forum for NowsSMS's product support, there are some very useful information here. - http://www.nowsms.com/messages/
GSM World on MMS - Articles on MMS. - http://www.gsmworld.com/technology/mms/index.shtml
JVending - J2ME MMS Client for Mobile Phone. - http://sourceforge.net/projects/jvending