skype, whatsapp, viber etc are proprietary, you need the other chap to have it on their phone be activated, logged in etc and I usually find that they're not without you using facebook, google messenger or even SMS to prompt them. For convenience I tend to use localphone, a voip rerouting system so you only pay the local call charges, quite nifty. http://www.localphone.com/ although i think skype may offer this sort of thing now....