I am currently using a configuration profile generated with the Configuration Utility in order to work around the internet access problem. It works fine for that, and I had no problem setting that up. I've had no problem with the service and no problem with configuring it provided that I had a place to enter the values that needed to be configured.
Back when I used the iOS 5.x modified-iTunes-backup procedure to modify the APNs, I found that all I needed to do was to change any of the default AT&T APNs to the "att.mvno" one and leave everything else the way that AT&T had already configured it for their service (including all of the default MMS values). So I haven't been using the Straight Talk supplied web proxy since day 1, and it's worked just fine. MMS used to work fine, too.
The thing that galls me about the MMS problem from a practicality perspective is that a friend of mine who doesn't own an iPhone could send me an MMS message, and not only would I never know that they sent it, but they would never know that I never got it. From their perspective, it was successfully sent, and nothing got kicked back to them. From my perspective, nothing ever showed up.
I also can't for the life of me imagine why the iPhone config utility doesn't have fields for MMS. It seems like such a strange and pointless omission.
I think that Apple has worked very hard to cast this image of themselves as the champion of the end-user. If that's the case, then they need to start proving it with mobile devices like the iPhone, which occupies a market segment where users have traditionally not been regarded as much more than pawns. I feel as though Apple here is treating this situation like their ongoing business relationship with AT&T and other carriers is more important than satisfying the needs of their customers whenever the two are in conflict. I suspect that Apple wouldn't want that kind of press.