Get SKYPE and as long as you have wi-fi you can make phone calls, you can also send text messages. Pretty cheap also. When I was on a detachment to Morocco a 10 dollar SKYPE credit lasted me a whole month and then some. But I wasn't on the phone 24-7 either I would make 20-30 minutes worth of calls every few days.
Edit- This was on an iPhone. I yanked the SIM card as soon as we left the country to avoid accidental international data charges which are VERY expensive.