[encoderer]

No, not so fast.

What you said -- "Google Voice numbers can only receive MMS from Sprint numbers" -- is true.

But if you're on sprint, you no longer need to use a "Google Voice" number. You just use your sprint number. It's able to verify that the number you type in is Sprint, and if so, it connects it behind the scenes to GV and disables any add'l GV number you're given.

When you do it this way -- the "proper" way to use GV on sprint -- then MMS pose no problem. ANYBODY can send me an MMS. It won't show up in the GV app unless it's sent by another Sprint user. If it's sent from another carrier, GV will ignore it and it'll show up, like any other message, in the native Android messaging app.