Didn't work for me at all.
Did exactly as you posted... even the mediaNet part..
Still not getting or sending MMS's..
Although, some people are stating that it takes a few hours or days and I just got done doing the steps. If it all of a sudden starts working I'll edit the post.
Damn I've been working at this for weeks now.
By the time I get this working Apple will have create an update that allows us to MMS anyway.
*edit - 20 minutes later I can't get into MEdiaNet anymore.. also, when I go to send a message, it gives me the "possible incorrect mmsc setting" error. Also, when I go into the outbox, the message has a big <not inserted> thing on the top. Super weird.
** edit 2 - I tested the app again 24 hours later.. still nothing. I notice the first post was edited to add a extra step when your in MEdiaNet. I repeated the entire process. Still doesn't work. Logged out of MEdiaNet and once again can't log back into MEdia Net. Sorry guys, I just don't see this working.
*** edit 3 - reinstalled the app and renewed the demo license (thanks for that swirly guys). I update the apn as stated in a two posts down. Changed UserAgent back to iPhone and still no luck. The message in the out box does have the recipients name in it (which was fixed from the reinstall) but I'm getting the same error "Possible incorrect mmsc setting".
NOTE: As soon as I change my SIM card back to the iPhone I am unable to log into MEdiaNet, regardless of making changes in the MEdiaNet account as stated in the directions.