You'll have no problems - both carriers - Verizon and AT&T (and the 'foreign' carriers') - have what you want and they do monthly plans too.
But there are so many free WiFi hotspots in the US that, when I travel there, (from the UK) I never bother to either buy a pre-paid card or use my home account 'roaming'. You'll find WiFi hotspots **everywhere** - malls, hotels, motels, coffee shops, copy shops (i.e. Kinko's), franchises (MacDonalds, Pizza Hut, Taco Bell, Starbucks etc etc), public transport, - almost anywhere. So, unless you're planning to spend time in a rural area, think about using WiFit - it it doesn't work out, you can always buy a pre-paid card.
Enjoy your trip to the US!!
Tim
Snowy Scotland