[T-Mobile, Samsung Galaxy SIII] flipster64:
UPDATE:

Just thougth I'd update this for anyone who stumbles on this thread in the future.

While everything about the phone from the outside and most of the stuff shown by Device Info indicated it was in fact a T999, apparently it did have an SGH-i747 bootloader. I overwrote that bootloader with an SGH-T999 bootloader, and hardbricked it.

So don't do that.

Talked to a JTAG-er who said that if the download screen says SGH-i747, it has an i747 motherboard.

Word of caution to others who end up with a refurb frankenphone.

I need some help understanding some things here. I'm a bit of a noob when it comes to this android stuff, though I have rooted my Nook once (then unrooted it) and I made an SD card for it with CM7 on it. And I have worked in IT since 1988 and have been a SysAdmin for at least half that time. So I do get most computer-related concepts and I've flashed firmware on everything from disk subsytems to my DSLR.

So here's my story:

I ordered an unlocked, refurbished Galaxy S3 off of Amazon. It's an SGH-T999 from T-Mobile, and T-Mobile is my carrier.

I noted something was awry when it wouldn't register to update. I also notice it doesn't have the wifi calling feature under settings, which it should have if it were stock. And that's a feature I used with my old HTC G2 a lot.

So I've been pouring over this forum for a few days trying to figure out what's up and what I should do to make it do what I want it to.

It has SuperSU on it, and the phone's status is "Modified". It's running 4.1.2, and the build is T999UVMD5-chag-multi-vT (it also lists a baseband version of T999UVDMD5 ... I'm guessing that's the modem version)

I assumed it was rooted because it has SuperSU on it, so I bought Mobile Odin to see if it would even run. It says it wants root (no shock there, but I thought I had it).

SuperSU says the binaries need updating, but it won't update them (it tries and says it failed). There's no SuperUser under "Settings", so I can't enable it.... so I'm starting to think it was rooted, flashed, then unrooted. Though the RootValidator app says I "might" have root since it was denied access. But SuperSu doesn't work right so I can't grant it SU permissions.

So first, I need help with a theory of the state of the phone. Frankly, it works great the way it is except I don't have the T-Mobile WiFi calling feature, which I'd really like. It DOES let me use the hotspot without an extra hotspot plan. Which is very cool (I don't use it much, but I like the option).

I've seen there's a 4.3 build out there based on the T999 that doesn't have Knox ... which I'm assuming is good from what I've read as far as being able to and keep root and control the hotspot feature. But I don't really know.

I've considered going back to an earlier stock version and letting it update OTA or via Kies, but then I'm afraid it might get certain things (like hotspot) disabled by the carrier. I'd really like to keep that feature.

But first ... how do I figure out if I have root on the phone already? I'm getting conflicting info.

Perhaps there is some kind knowledgeable soul who can help me find my way.

Much appreciated if anyone can help.