mms and visual voicemail don't work when connected to wifi

iphone6, ios 8.0.2, tmobile (california), uverse (home internet)

I've noticed that i cannot send/receive mms (pictures) and visual voicemail notifications don't come through when connected to my home wifi (att uverse). I have not tried other wifi networks, but my home network didn't have this issue with my old iphone 4 a month ago. i have imessage disabled.

if i turn off wifi on the phone, mms will send, and after a while i will even start receiving old mms messages from when wifi was on. I also tried a network reset, and after the reboot, i got 8 mms from yesterday, and a visual voicemail from 2 days ago. after i reconnected to my wifi, mms didn't work again.

again, mms/vvm are fine on the tmobile network, it is only with wifi enabled that it stops working. hard reset also didn't change the behaviour.