Google is currently testing a feature of VoIP (Voice over IP) which will make part of future Gmail. More specifically the Gmail Chat application.
Google has set up phone booths across America’s colleges and airports as it launches Google Voice Integration with Gmail.
Users will be able to make calls from Gmail to contacts mobile phones from the Chat application list.
Initially, the service will be available only in the United States and Canada. If Google wants to compete with Skype, they will have to enable the VoIP service globally. The calls will not be free, but will be very cheap.
VoIP feature will be introduced in Gmail following the acquisition of Gizmo5 service, last year by Google.