Handcent MMS Question

I've got a question for anyone who uses handcent on the regular.

On my old phone (Galaxy Nexus on Sprint), when i sent an MMS, it would send over wifi, never thought twice about it. I switched carriers to AT&T, and upgraded my phone to the GS4 Active, however, when i send an MMS with it now, even while on wifi, it will send it through the carrier instead of through the wifi. I've gone through every setting i can think of at least ten times, is it something with the carrier, or the new phone? someone please offer me some insight.