However, I really can't sympathize with you at all. You intentionally and knowingly chose to do something that was not officially supported. Now you are complaining that your hack stopped working. If you wanted it to always work, you should not be doing something so weird.
Classic case of "Doctor, it hurts when I do this."
It's not so much an "unofficial workaround" as a mandatory component of the unlocked device.
If you put in a SIM card that the iPhone has no clue about (such as T-Mobile U.S.)., then iOS will fall back to a generic carrier profile, which does allow access to the APN editing submenu.
The problem is that Straight Talk is an AT&T MVNO, and so Straight Talk SIMs are indistinguishable from AT&T SIM cards from the iPhone's perspective. The iPhone engineers made a bad assumption, which is that all cards issued by carrier X should be treated exactly the same.
...I still think APN blocking is entirely irrational on the part of the carrier. There's no way a user can subject their carrier's network to fraud or abuse by having access to the APNs (http://forums.macrumors.com/showthread.php?p=16266682#post16...)
1. Get SIM card.
2. Buy "unlocked" iPhone.
3. Put SIM card into "unlocked" phone.
4. It doesn't work! :sad-face:
5. Google around.
6. Find solution.
7. Implement solution while grumbling to self about truth in advertising.
8. It works! (hooray)
9. Software update breaks solution.
I still say the key word here is "unlocked." If Apple truly meant for the "unlocked" iPhone to only be used with supported carriers (and then what's the point? you think Apple's really only selling "unlocked" phones to international travelers?), then they shouldn't be using that word to describe it.
Just by comparison, Android supports on-device APN editing (see Settings -> More... [under Wireless and Networks] -> Mobile Networks -> Access Point Names).
T-Mobile actually encourages users to edit their own APNs for IPv6 support, and has run an IPv6 custom APN beta trial for a while:
I didn't alter any cell based network settings. Though I recall the output file from the iPhone Configuration Utility was merely a text file. I believe, though I'm not 100% certain, and this was around iOS3-4, that I opened the file in a text editor. I think I recall this because I came to the conclusion one could make a web based configuration utility that output the same data file.
I'm pretty sure it was just simple XML. It may be a binary plist type file now, but plutil should solve that problem.
Couldn't one manually edit the output file to contain the values they desire, import the file, pop in the SIM, and have a functioning iPhone on iOS6?
Just a thought based on some very old memories. Anyone care to fire up iPhone Configuration Utility and see what file type it generates. Even if not XML, a hex editor should allow the changes, no?. A small git-hub project could probably create all the needed profiles for the various carriers out there for unlocked phones.