Being cost-conscious budget travelers, we look for for free Internet wherever we can. We've installed Skype on our netbook and it works well in, for example, our hotel room. We use our AT&T GSM quad-band phone for text messages at about 50 cents each, or for urgent or emergency phone calls, at a cost of anywhere from $1.29 to $2.00 per minute, depending on the country.
The cheapest way to access wireless service abroad only works if you travel very frequently: You carry an "unlocked" phone (one that will accept any SIM card) and you buy the cheapest card you can find for each individual country in which you're traveling. Where to find the best ones is the subject of discussion in travel forums such as this FlyerTalk thread.
If we ever decide we really need wireless voice or - especially - data service in our pocket, we'll probably buy a package from a specialty outfit such as Telestial. A key feature for us would be free incoming calls in a variety of countries. Buried somewhere in the fine print is the fact that there's usually a time limit on the airtime you buy. If you travel to Europe next week but don't return there for another year, chances are your time will have expired, greatly increasing the actual per-minute rate. You can get fancier and subscribe to an international callback service, which enables you to trigger access to a U.S. callback number and then call the U.S. from, for example, Germany for about 37 cents a minute. Telestial's add-on "Return Call Service" may cut that rate in half, but that's still 17 cents a minute in addition to the per-minute rate on your SIM card.
David Rowell goes into great detail about the plethora of options in a typically detailed multi-part Travel Insider article. The bottom line? As far as we know, there's still no perfect way (for us that means cheap and easy) to access wireless service in foreign countries. The trick is to figure what's going to work for you.