I have bought an unlocked LG Optimus G Pro and am using it on T-Mobile. It's on JB version 4.1.2. I know AT&T has rolled out KitKat upgrade for Optimus G Pro. I tried to update the software on my phone but it kept saying "Phone not registered to network". I went to LG support page and they redirected me to AT&T for software upgrade. There is no manual download link for the upgrade and AT&T page says it will happen OTA and must have active sim card in it[which I guess means Active ATT sim card].
My question is:
->Is it possible to upgrade it to 4.4.2 version that AT&T has pushed without being on AT&T?
->If so, where can I find the stock/untouched 4.4.2 ROM?
Thanks in advance. Sorry, if this is a repeat question but I did search the threads and didn't find this question anywhere.