Still no outgoing MMS support, but it's a step in the right direction
Google announced that full MMS support will hit Google Voice in early 2014, but it has made at least one small step towards that goal today by adding T-Mobile MMS receive support. Just as has (theoretically) been the case with Sprint for some time now, Google Voice users receiving an MMS from a T-Mobile customer will have that picture emailed to them. You'll get a simple "MMS received" email to your Gmail account, along with the picture as an attachment, and you'll also get an SMS indicating that the picture was received.
There doesn't seem to be any noticeable delay, and we've just tested it ourselves and it seems to work just fine. Now this certainly isn't the most elegant solution ever, and it doesn't help us with outgoing MMS from Google Voice numbers, but it at least means that now when your friends and family send you pictures you'll get them if they're on Sprint or T-Mobile.
And now we play the waiting game until full-on MMS support comes to the service.
Source: +Alex Wiesen