My unlocked Samsung Galaxy SII didn't switch yesterday. I turn my phone off overnight, so I didn't think a power cycle would fix it. Finally last night I set the time manually. When I turned it on this morning I changed it back to use the network time and it's been fine since.
@Furkmyster iPhone thread no one questioned your Samsung.
Well, I responded about my Samsung so the OP would know that it wasn't just an iPhone problem.
The power cycle is probably what did it, but from other forums I've seen repeatedly turning automatic on/off works too. I was ready to blame MTS for it, but clearly some phones are just more stubborn than others.