It looks like AT&T has quietly introduced a 10-cent per minute prepaid plan. I am not sure, but it seems that you simply pay a flat 10 cents per minute, and the minutes don't seem to expire every month or two like Net10's do.
Another big plus is that the AT&T GoPhones seem to work in Mexico and Canada, offering reasonable rates. Here's a link:
http://www.wireless.att.com/learn/international/roaming/gophone-international-roaming.jspThe above link shows rates to use AT&T GoPhones in Canada and Mexico. The rates for Canada are 0.39 per minute. These are AT&T's prepaid phones, pay by the minute.
You can buy a phone for $20 and just keep it for your trips to Canada and Mexico. I think I am going to do so. I have an unlocked Blackberry that I used to use on the T-Mobile network, which is GSM, as is AT&T's network. I ordered a SIM card that will hopefully work on the AT&T GoPhone network in my old Blackberry. I'll post to this blog how things go in Canada with this phone.
My other recommendation for folks who want an inexpensive, prepaid plan with emails is to purchase a Blackberry at Walmart that works with the Virgin Mobile network. These cost $100 now, and the Virgin Mobile network will then work with the Blackberry for only $35 per month for unlimited data and 300 talk minutes. (To get Blackberry email and web browsing, you have to pay another $10 per month above this). Pretty good deal, but if you need to use your Blackberry internationally, you will have to go with AT&T's contract service (like most intl travelers that I know). As far as I know, the Virgin Mobile Blackberry service won't work outside of the US.