Traveling two weeks in Washington/Oregon

[Telekom]

Originally Posted by Chen

Hi all, I'd appreciate some help with this - I'm traveling in a couple of weeks to Washington and Oregon, doing ~10 days in the car hopping between the natural parks of the two states.
I have Xperia U and Galaxy S II smartphones and a Galaxy Tab 7.7. Would like to purchase a prepaid SIM mainly for data usage on either one of the phones or the tab. To call home with Skype, send some mails, check the maps, etc.
Which carrier would you suggest both in terms of price and coverage in those areas?

Thanks!!

Your only choice for SIMs are AT&T and T-Mobile.

[rfranzq]

Originally Posted by Telekom

Your only choice for SIMs are AT&T and T-Mobile.

And not any MVNOs? Why? not?