Theonly thing that you might expect is wiretapping. You should pretty much assume that the government is listening in on all phone conversations. They might not be, but there is nothing to keep them from doing it.
If you do annoy the Chinese government, all they are likely to do is to cancel your visa and kick you out. For that matter, the fact that they've even issued you a visa means that you aren't on their "bad people's" list.
Finally, the Chinese government won't mess with people randomly. If the government randomly targets people, they what possible reason to you have for doing what the government wants you to do. The way the system works is that if you don't oppose the government, they won't do anything bad to you, but if you do oppose the government, bad things will happen to you. If the government randomly beats people up, then you have no reason not to oppose the government.