Just a quick note to mention that MAXRoam.com is a really great service. Essentially it’s a reduced rate pre-paid SIM card that lets you add multiple numbers to the same SIM. For example, I now have a SIM card with four international numbers in Spain, Poland, Germany, and the US and they all work seamlessly in almost any phone. It basically lets locals call you at local rates and you call at almost local rates when in country.
The card costs 29.99 euro with a 5 euro call credit and new numbers cost 5 euro a month. The plan is fairly simple: you buy the SIM and make calls. Then, when you travel, you add a new number to the SIM for a month or so and take it off when you’re done with it. MAXRoam has a web-based system for topping up and adding numbers. A bit pricey but it works very well.