Select 'Receive incoming calls' in Android, even if you disabled it in the FritzBox. Look your IP address up using a site like

Using 16 random digits, you can safely enable the 'Allow registration from the Internet' feature in the 'Account Information' tab in the FritzBox. Tip: after entering the password in the fritzbox, copy it to notepad and format the numbers into groups of 5 to make them easier to type into your Android device. Advised length is 16 digits because hackers can guess numbers more easily (a strong password should have letters, but the FritzBox cannot do that with for VoIP/SIP). Pick a random password that is only numbers. Choose Telephone in the first step and LAN/WLAN (IP telephone) in the second step. The FritzBox password can only be digits.įor future reference, these are the complete steps:Ĭreate a new telephony device here: (you will need to log in to your router). After about an hour of searching and debugging I've found the answer: