We're planning a vacation for next year and I've been thinking (among other things) about phone access. The last time I went out of the country, to Florida in 2003, I spent about $50 in roaming charges for a pretty small number of minutes of airtime. It was almost $2 a minute to receive a call and well over a dollar to place a local call... pretty obnixious. (I'm on Rogers, which is a GSM network, but Telus, SaskTel, Bell, etc. all have obnoxious roaming rates.
So I've done some digging... and some ordering. I've gotten some SIM cards for GSM prepaid providers in the UK (O2) and the US (T-Mobile). Both are cheap to run and cheap to keep up. O2's time is good for up to a year and you can top up your account to keep your prepaid time going. T-Mobile requires you to top up regularly but if you buy a $100 card first, you only have to add $10 every year to keep it going. O2's rates will be about 25 pence a minute for the first three minutes a day, and 5p after that, which is very reasonable; incoming calls are free (they cost the caller about 20 cents a minute, even from North America). T-Mobile costs about 10 cents a minute including long distance.
I also discovered that PagePlus is a very cheap American CDMA-based prepaid plan that works in Canada. It's about 10-20 cents a minute on Verizon towers, and 99 cents a minute on other providers' towers. The service works on SaskTel. I tried it. ($5 US and half a day... check out eBay for some reliable sellers.) Kind of expensive to use here in Saskatchewan, but great for an emergency phone, especially if your main phone is on Rogers or Fido and you want the big SaskTel coverage footprint... and it works very cheaply in the States. Just buy an old Verizon phone. :)