For the US most providers have tolerable pay as you go voice and messaging plans. I have used ATT.
But, I am one who doesn't use voice a lot. I much prefer to use email first, and then messaging, to stay in contact. With Gmail I can manage all my email accounts. This type of data is what I would like to find for trave in the US.
In Mexico I have a basic Telcel pay as you go that I can keep active for very little money. Then when I am in Mexico I buy a 30 day data package for my smart phone, and can carry on using email and Web browsing the money I deposit every two months pays for the data plan. I just swap SIM cards in my unlocked smart phone.
