Have used Viber but the connections when calling back home break more often than not. Was thinking about trying Global Call so checked their FB page. They have this cool contest going on wherein they will sponsor a round trip air ticket of yours (https://www.facebook.com/uglobalcall/app_193371724140087) so it does come across as a decent VoIP app. If anyone has used it, then please share your experience.
App Link - https://play.google.com/store/apps/details?id=com.lguplus.GCAClient
App Link - https://play.google.com/store/apps/details?id=com.lguplus.GCAClient