I am planning to buy an IPAQ 6315 either from www.amazon.com, www.pcnation.com or any other store online. But i am planning to not buy it with a phone service provider nor activaded with any company. So this product is going to cost me about $590 i think. The reason is because i am going back to my country in 3 months, and i do not need a cell phone service provider in the US. Will the phone work in my country (Mexico) just by putting a SIM from Mexico in the phone? Do i need to unlock the code of the phone, even if i am not with any phone service company? What is actually to UNLOCK THE CODE of the phone?