1) It may be cheap relatively-speaking, but why should I have to spend anything above and beyond what I already spent on this unlocked phone just to make it work the way it should? (I know, I know...this is one of those "it's the principle of the thing" arguments.)
2) It's another glitch, much like the one I used to rely on in iOS 5. And like that glitch, it will surely be fixed by Apple in the future. I need something that is reliable and that I can count on.
3) Speaking of reliable, the jury still seems to be out on how reliable it is. It does seem to stick around for a number of people, but I have read a handful of anecdotes where the APNs were mysteriously reset somehow, and the person would have to re-do the trick. I don't like the idea of having something like that randomly flake-out on me. Plus it would mean that because I'd never know when it might stop working, I'd have to carry that darned T-Mobile SIM card with me wherever I go, "just in case."
I'd rather Apple just fix the issue the right way. A quick software workaround like the one I used in iOS 5 is one thing, but if I'm going to have to resort to jury-rigging something in meatspace, then I might as well drop Apple and switch to a different phone at that point. I'm already considering it.