This week we played around with an E815, an E816 and a V3M all flashed. The only way we could get the MMS to work on any of them was if we added unlimited WAP to the acct.
Without enabling WAP, the MMS would look like it was working but only "send" 90% (give or take a few %) and then error out. This held true for all 3 phones.
We could open the WAP home page (didn't try to go any further), but MMS would not work on a non-WAP enabled acct.
It doesn't make any sense, and it was EXTREMELY frustrating trying to figure it out, but that's what we found.
Your mileage may vary.