I got mine unlocked middle of last week through unlock_fusion. iPhoneox.com showed the unlocked status at the time. I didn't go through the restore process at the time, but after seeing this thread, I restored my iPhone, and I never got the "unlocked" message in iTunes. In addition, iPhoneox.com now shows my phone as "locked," so something has changed since last week.
I went to a T-Mobile store, and they popped in a SIM card that they popped out of a credit card sized thing. An apple logo splash screen came up upon restart, and said "activation required." then, it tried to find wifi (or connect to iTunes at the bottom). I couldn't do that at the store, so I exited out of the screen, and in the top left corner, it said "No service." So the T-mobile rep took that to mean that the phone was still locked. It didn't say "invalid SIM" or anything else.
Waiting for a return reply from unlock_fusion.