While in US I had a prepaid ATT sim card for voice and for data I purchased a Mi-Fi hotspot device and a PAYG data plan which everybody in the group was able to share.
The plan I chose for voice was the $2/day unlimited US nationalwide outgoing and unlimited incoming, for canadian cand overseas calls I used my long distance provider (call select) with a US access number and payed decent rates 2-3 cents/minute, the access point being US was part of the unlimited thingy. $2 is paid only for the days the phone was used, aka first call = $2, all the subsequent calls that day = $0.
For the data I opted for the Verizon 1GB plan, valid for 30 days, $50.