AT&T UNLOCKED SGH-I747 4.1.1 shows no OS updates

[Android Question]

I just purchased my first andriod phone : a new UNLOCKED AT&T Galaxy S3 (SGH-I747) running 4.1.1 and using it on the t-mobile network...

When I try to update the OS (from the AT&T servers- only option from phone), I receive "no updates are available"
When I try to update the OS using KIES, I receive "current OS is 4.1.1 - your version is 4.1.1 - No update available"

Is there any way to update the OS to at least 4.3? I have heard updates to 4.3 have been rolled-out for some time now for AT&T as well as T-Mobile.

Also, I'd like to be able to use WiFi calling (since I am using this phone with t-mobile). Is there a way to do this?? Can I use a modified ROM for t-moble handsets? I'm pretty sure the AT&T S3 and the t-moble S3 use the same dual-core CPU and hardware...

Thanks for any help you can provide. Cheers!

 

[Rukbat]

1) First read the 4.3 horror stories all over the web. You may not want to update.

2) It's an AT&T phone. Unlocked or not, it'll only update OTA (over the air) when registered on the AT&T network.

3) Wifi calling is a function of both the hardware in the TMobile phone and the TMobile network. Since you have an AT&T phone you can't do Wifi calling.