hoow can I make and receive calls With USA and Canada by using a PBX account, Acrobits softphone, and Google chat? I have an iPhone 4s running iOS 8, I an recently using it in the Middle East, but I would like to make and receive calls to people living in Canada and USA. I have a gmail that has an American mobile number connected to its Google voice. Is their an app that would enable me to make and receive phone calls by using this American phone number to my iPhone. But I don't have the sim for this American phone number, and my iPhone has a sim with a local number from the Middle East installed to it.
I've had good luck with Acrobits Softphone... it's a SIP soft phone for iOS.  Once you have an appropriate VoIP/PBX account that supports SIP clients, you can use google chat to get your calls into the PBX.

It definitely has some noticeable lag, but it is certainly better than nothing.  

You can get a free VoIP/PBX account at pbxes.com (I have no affiliation).