I now am now using Straight Talk prepaid instead of AT&T (for $41 total monthly I get 2.5 GB 4G data, unlimited talk and text. And because Straight Talk is an MVNO carrier, I am using AT&T's towers on my phone! Go figure.)
Anyway Straight Talk's SIM program is where one buys a SIM from Straight Talk ($15) and can use that on any AT&T GSM phone, from an old model or the SGS III.
When putting the SIM into a different phone you have to manually enter the APN info. Straight Talk's site tells how to do that and I saved the settings on my computer too.
I was setting up my GF's phone for use on Straight Talk. She got a used (like new) AT&T HTC 4G Inspire for $100 (that's a good deal). When I went into Settings to enter Straight Talk's APN info I noticed there were two lock symbols next to two APN entries. (I believe that means the APNs are locked by the carrier. Not sure, but if you get the phone unlocked that gets rid of the locks.)
Anyway, I spent about 20 minutes trying all kinds of ways to get the Straight Talk APN to work and it would not.
Enter that Tweakker program. I downloaded that from Android Market (using a WiFi connection to the Inspire).
WARNING: This program apparently uses a WiFi connection to access the Net, perhaps to get to an online settings database?
I had WiFi turned off, when I opened Tweakker it turned on my WiFi connection (to access the latest list of APN settings?).
Tweakker then asked what carrier's APN do I want to set up (I picked Straight Talk U.S.).
Tweakker made the changes. It then said words to the effect "Checking the network connection, this will take about a minute."
It turned OFF my WiFi. About 60 seconds later I was connected to the Net, with a 4G connection. I checked the settings and the two padlocked APNs were GONE! Instead there was only one APN on the list. I checked the settings and they were the exact APN settings Straight Talk provides on the Net, in its support section.
Can't complain about that (I especially wanted to get rid of those locked AT&T APNs. (IMO even if it cannot get rid of those APNs the program would set them up so that Straight Talk, in my case, is the default APN used.)
By the way, this particular HTC 4G Inspire (again, it is an AT&T phone) is rooted, but NOT unlocked. (If you get your phone unlocked I don't think it matters which Android version you are using, you can change the APNs with a program like this. IMO this is so because that's the whole point of getting a phone unlocked, you can use any carrier's network.)
This phone is running Android 2.3.3 (Gingerbread).
Hope that helps, and that my opinions are correct.

