Why do I have to upload my address book to Rebtel when I start using the application?With Rebtel, you don't need to come up with a clever user name, and you don't need to build up separate buddy lists for friends you want to call for free. Instead, Rebtel lets you call anyone in your contact list also running the app for free and it immediately lets you know when one of your contacts have started to use the application. Your contacts are securely stored and we never sell or share this information with third parties.