​ENUM can be used to translate telephone numbers into IP addresses, much alike ​DNS is used to translate domain names into IP adresses. This makes point-to-point telephony possible (for example from Fritz!Box to Fritz!Box), bypassing (internet) telephony companies. For this you need a working SIP server. You can read ​here about how to setup a SIP server and ​here about changing the ENUM servers (both in German).