A little off-topic, but have people been able to get "Internet Sharing" to work on T-Mobile US using the SGH-T899M? It refuses to work for me (claims there's no mobile data connection to share... even if I'm streaming music over that exact connection at the very moment). Here's what I did:
Bought a SIM-unlocked SGH-T899M handset off of Amazon.
Pulled the T-Mobile SIM (which had originally provided a contract plan, but had been switched over to their new $50 unlimited plan which includes 500MB of tethered data/month a month prior) out of my HD7, cut it down to MicroSIM size, and installed it.
Booted the phone up, noted the immediate recognition of the T-Mobile network including the HSPA+ 4G (no LTE in my region yet, but it's coming).
Tested the data connection; it worked great.
Opened the Internet Sharing Settings app, and tapped the toggle.
Got the "Connection not shared: There's no mobile data connection to share at the moment. Check your mobile settings and signal, and try again." error.
Checked the mobile settings (including APN) and signal, and tried again (same result).
Rebooted the phone, set the APN manually, and tried a number of other things (same result).
Took the phone to T-Mobile, they set custom APNs, tested settings, and tried again (same result).
Replaced my old (originally 3G MiniSIM) with a new and modern T-Mobile MicroSIM.
Booted phone with the new SIM, tried the data connection again (still worked) and then Internet Sharing again (still didn't).
This is getting really frustrating... My next step is to take it to a MS Store (I'm lucky enough to live near one) and they said they can spend a couple hours running a battery of tests on the phone, but I'd really prefer it if there was a fix I could do myself...
Thanks in advance!