The internet data apn is att.mvno while mms goes through Cingular. That's from a custom apn I added for Straight Talk. The phone also has an ATT apn it created by default when I put the ST sim in it and that apn can't be deleted, just inactivated.
Sent from my RM-937_apac_hong_kong_222 using Tapatalk
My assumption is that the ATT/ST sim adds one of 2 things.
1. A hidden tethering APN that we can't reset b/c we do not have access to the registry, nor to tethering APNs
2. A flag that tells the phone to check with ATT's servers to see if your phone number is recognized before tethering
The proposed solutions that I have seen are to flash a foreign keyboard, or trooter's method of using a foreign SIM to reset the APNs. Both of which have been successfully used by people who bough ATT phones and are using them internationally (the opposite of our issue). This weekend I may try some ROM flashing to see if on some whim I can get anywhere with a different ROM and one of the two hacks mentioned above. What really annoys me however, is that I hate Android exactly b/c it NEEDS to be tinkered with and maintained for the phone to work properly - so having to go through this on my WP is very annoying. If it weren't for the fact that Android's UI is a complete reprehensible mess with no attention to user experience, and a lack of hyperlinking w/in OEM applications such as being able to access call history of a contact from a text message, I'd probably just switch back.
I don't know what Telegence (TLG) is, but both the OP and I were able to tether using international Android devices on our networks. So unless Telegence is activated on the phone side, it should have also restricted our non-ATT Android phones from tethering as well.