Rebtel uses Apple's push notification service to notify you of incoming and missed calls. So in order for your friends to be able toc all you for free, push notifications need to be enabled for Rebtel on your iPhone. To enable push notifications, go to your iphone's Settings application, then select Notifications. Ensure that Notifications are activated then tap Rebtel and set all sliders to ON. You’re now ready to use the Rebtel iPhone application!