I would strongly advise against using 3 in the US, there speeds whilst roaming are absolutley diabolical, and worse than o2, and having used both o2. 3 and vodafone in Nevada, Hawaii, New York, Washington, NY and LAX the best network was Voda..
3 struggled on t-mobile
o2 on AT&T was usable
Voda just worked at good speeds on AT&T
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