I want to but GW2 and interested if it is possible to play from one account on servers from different regions (EU, USA and etc.). Is there any limitations for one account, like to play only in one region servers? Does the account has some kind of region lock?
With one account you have one Home World. You are only able to change this if you pay gems (500 low population, 1000 on high population or 1800 if you want to play on high population server).
But you are always able to play on a other server as a guest (but only in the same region means NA or EU).
Guesting allows you to temporarily change your associated world, thus affecting one of the factors affecting which instance you are placed in. It does not allow you to play for a different team in World versus World. Due to the megaserver system, most players will never need to guest.
To start the guest mode you have to click on the Guest button for the world you wish to guest to and confirm your choice. The game will place a suitcase icon symbol next to the guest world.
Read more on the guild wars 2 wiki.