[GadgetKen]

Have not traveled to Alaska but other family members have.

AT&T or local carriers are probably your best bet. However, 3G or better data coverage will be best in southeastern Alaska in the Anchorage, Fairbanks and Juneau areas (plus probably a bit of coverage on the north shore). Data coverage outside those areas is more likely to be Edge or slower speeds (at least by looking at coverage maps on the AT&T and GCI websites). You might want to consider getting an AT&T GoPhone sim card and setting it up with a data plan (or using a GoPhone sim card in a mifi device). AT&T GoPhone sim cards also roam in Canada at reasonable rates. Or get a local prepaid sim card when you travel there.

As far as I know, Verizon, T-Mobile, and Sprint all function in Alaska only through roaming agreements with other carriers...and those would work better with postpaid rather than prepaid.

If you plan on being in rural areas in Western Alaska, you might also want to consider renting a satellite data modem (thinking perhaps Iridium over Inmarsat or Globalstar). Satellite data is slow and expensive but at least it would work in rural areas without mobile phone towers.

Enjoy your trip to the USA!