Could you help me with my mobile question?

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Hello! I hope you all can help me. In 2005 I bought a pre-paid Sony Ericsson phone from Movistar in Spain. I know it can work in UK, Portugal, Spain, and basically almost anywhere in Europe at least that's what the box claims. I know it worked in Spain, France and Portugual as I traveled through those places and it worked. Now, for people in USA/Canada/Mexico, as you know my phone as a SIM card and it doesn't work. It says "No hay red" which means "Can't find network." I know there are some companies like Virgin Mobile (I think) that uses the same signal as European mobile phones. So here are my questions for you, is it possible to use this phone in USA? Is it possible to still use in Europe when I go back? (It's been almost 3 years). Should I sell it on eBay so someone else can use it? What type of phone do you think is better prepaid (pay as you go) or contract? What type of phone plan do you have? Thanks! Pablo