I am very very pleased with FriendCaller, I want to recommend you, they are very cheap ... (call from 0.02$ world wide)
Read their site ->
FriendCaller - Free Video Chat and VoIP calls for iPhone, Android, Mac, PC and Linux
greeting
My favorite sim and VoIP for roaming in Europe and worldwide:
UWT-mobile and Xxsim: for call+sms in Europa extern and Worldwide
ToggleMobile: for internet+call+sms only in EU intern
(VoIP/Sip) FriendCaller or SipCall.ch: Worldwide sms+call