If i am headed overseas for any length of time for like a couple of days. What I like to do is go to a news stand and buy a local sim card (the card that inserts into the GSM phone). Make sure you have a Tri mode gsm band 850,1800,1900. This will cover you in all cases. Since 1900 is only usa. Still though some companys tout a gsm phone but it's only 1900 making it unsuable overseas.
I keep a local sim card when i'm making calls back to the states. You can recharge the sim card at any shops and just enter the number on the card and it puts another 50 bucks on the sim.
I also use ATT international calling. They send you a sim card for 25 bucks and you can use it overseas. That way you can recieve calls from the states on your cell phone. Only problem is if you get a call and it goes to the voicemail you still get charged. Thats a pain in the rear.
Tmobile offers a good plan. Currently I'm waiting for a GAIT phone to come out from att. They have the t62u but i'm not impressed. Gait is amps, digital, gsm, and tdma. That covers all spectrums which is what we really need as pilots who go to bfe.