I currently have cellular service with T-Mobile USA and will be visiting China for 3 weeks in April. I have unlocked all of my phones(HTC 8x, IPhone 4S, Lumia 521) for my family and plan to purchase sim cards in Beijing upon arrival. We will be staying in the following cities: Beijing, Shanghai, Chengdu, Chongqing and Kunming. Not sure what would be long distance charges and hopefully there are no roaming fees as I was told China Unicom should have good 3G coverage in all of those cities. Will we need to purchase new sim cards in each city or can we continue to use the sim cards purchased in Beijing in the other cities? Prefer to keep same number for entire trip if long distance fees are reasonable.