I've been a happy user of telestial HopAbroad card. It has worked flawlessly for me in many countries (they list 70 as the number of countries it works in). Its not particularly cheap (.35 incoming and about $1.00 outgoing), but with my travel pattern (heavy leisure, mutiple counties, not a lot of heavy useage in any one country), it has worked very well. No question that it is cheaper to buy a local SIM, but when I'm in a country on leisure travel, I rarely spend more than 20-30 minutes calling home in that country.