Do I purchase mobile phone in USA or Guangzhou?

Hi I am moving to Guangzhou in August 2016, I've been trying to read up on the subject and would love some input.
I think I've read that I need to buy or bring an unlocked cell phone and then once in China just purchase the China SIM card?? Is that the best way?
What about internet providers any tips?:
Thanks so much :)   Suzanne

I can't offer much as far as the service providers go, but perhaps a couple of things to watch for with the phone.
You've already mentioned the phone must be unlocked, a good start, but also check the mains adaptor's input voltage.
All USB chargers have an output of 5 volts at 1 or 2 amps, but I understand many US units only operate with an input voltage of 110v, not the universal 110 to 240 the rest of the world are supplied with.
Not a serious issues as you can simply buy a new charger when you land, but don't plug the old one.

Thanks :)

I suggest you buy one in Guangzhou directly, maybe you can get a cheaper price on iPhone in USA, if you use Android phone you should absolutely buy one in China cause there are so many choices than in the USA, Mi, Meizu, Huawei, OPPO, Vivo etc. Samsung and LG are not suggested. :D