Depending on what province you stay in China does limit your connectivity elsewhere. My experience with a pay and go mobile whilst all over the mainland was interesting, to say the least. Issues calling certain numbers were noticeable, as well as using certain types of calling card. Whether a feature works from one city to another seems to be a matter of knowing the exact infrastructure in each area, which naturally the casual traveler will not. Daily random text adverts are common, particular when changing city or province.
The pay and go SIM I had was gained through a Chinese friend who happened to have a China Mobile contract, so it would be unfair to say I was given different treatment, as I had no involvement in purchasing the SIM card.
I had previously thought all mobile operators were owned by the Chinese government, but some searching has revealed this is untrue, which surprised me, given the country enjoys monitoring people, to a similar level in which the British are monitored.