Recently if you have found that you cannot place a call using Rebtel PC app and getting the error "It is currently not possible to make call" then you should try other calling methods with Rebtel without reinsalling their application.
Call from your iPhone, Rebtel Android or blackberry phones using rebtel app.
Call from the Rebtel access number.
Rebtel is fixing this problem and will resolve soon. Please write your comments if you are experiencing this problem for long time.