Originally Posted by loneBoat
Thanks for the suggestions. I opened the testing window via my dialer, and the selected option is "GSM/WCDMA/LTE auto". So SEEMS like it should automatically get on something other than LTE. Weird.
The switching does not always happen correctly, its a known issue on AT&T's network on this and other devices (although I haven't seen your specific problem before, with data and voice not working simultaneously).
You can also specify some network types in Settings>Mobile network>Network mode (without the dialer code) on CleanROM (its locked out on stock the AT&T ROM). Try to force WCDMA and see if that helps.
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Phone: HTC One X (AT&T version) Rooted, Bootloader Unlocked, S-Off
Tablet: Samsung Galaxy Note 8 (WiFi only) Rooted