I realized that if you intend to download app / games from App Store or 'other sources', even 3GB is not enough because iPhone app / games are HUGE! Game easily is 200MB, even GPS software is 200MB! Therefore, I advice new iPhone users to download via WiFi whenever possible! By doing so, 1GB or 3GB makes not much difference as regular usage like surf net, facebook, youtube, GPS will not even exceed 500MB.