Was in multiple cities in China a few weeks ago and phone kept defaulting to China Mobile.

On manual scan for China Unicom it wouldn't fail but would just timeout trying to connect. Then on 5-6th attempt it connected fine and stayed there for the rest of the trip.

Speed/performance was MUCH better than China Mobile.

So to all those who are often in China don't know if China Unicom has issues in timing out SIM authentication to T-Mobile or what but it DOES work but you may need to make multiple attempts to connect to China Unicom (possibly set phone to 3G only)