WCDMA 3G Question

[Bigwidge]

I want to buy a tablet with GPS, WiFi, and 3G capability. The tablet I want has WCDMA, based on GSM technology for 3G service. I would be using this in the USA, and I am unsure of what provider would be needed for the 3G. Can somebody tell me which provider would need to provide me with the 3G service? I just dont know who to call and ask out of Verizon, AT&T, T-Mobile, Sprint, etc.