Do you check whether your phone is connected to the router? Is your DECT phone registered with the router? Is it possibly an IP connection issue? Is your phone at all appropriate for SIP telephony/logged into the router? Is the access data entered correctly? Do you need a splitter or possibly a terminal adapter? These issues should also be described in the operating instructions/installation instructions for your device. If you need help or don't have time to troubleshoot, you can book a Mila service partner.
With wireless internet (WIMAX/WLAN/LTE), only the new PC/laptop/netbook has to be connected to the existing router. With a WLAN connection, you have to have the SSID and password ready.
A terminal adapter is always necessary if a phone isn't suitable for SIP telephony. It may be cheaper to buy a new phone with the additional functions instead.
In principle, it's possible with DECT phones. You have to connect the phone to a PC via a USB and find the phone memory. The new ringtone can be loaded there as a WAV file.
Connect the base station of the wireless phone to the router. If the router also functions as a DECT base station, you have to activate that function in the router and open the menu item "Connect to base station (router)" on the phone.
Modern routers usually have at least two sockets for phones. Simply connect the new phone to the free socket. You may have to reassign phone numbers in the router menu.