There are few application to make a call from any where to any where by using Viber, Tango, Skype applications for smart phones only. These free services/application is for Iphone or Android. If you using WiFi then it would not use your data plan. IF there is no WiFi then application will use data plan (if data plan is unlimited then it is OK) otherwise phone company will charge for usuage so be carefull for this. 
