Yep. Working very well on T-mobile where I am. I got the RM-985 from B&H Photo.
This thread has been really informative.
I've gotten tired of spending the last 4 months getting calls from Microsoft to fix internet sharing/music playback on my Lumia 925, so I'm thinking about getting an 830 (that, or just going Android) for T-Mobile. And then you'll be able to use internet sharing?
So it's as simply as getting an AT&T Lumia-830 (RM-985, NOT 984) off eBay or an online retailer, and calling AT&T and presenting a receipt, to have an unlock code? Will they even do this if you're not an AT&T customer--that's surprising, since calling T-Mobile, the first thing they ask is for your account with them.
What reason do you need to give? Can you just explain to them that you want to use one of their phones on another plan? How long does it usually take for them to give you the code?
If it's that simple, I may pull the trigger on one off eBay. I live in the United States, so a more expensive but "safer" option might just be buy one from an AT&T store, without contract--they'd have to support their own sale, right?