The best thing is to ask UPC directly, otherwise it is usually apparent from the router details on the Internet.
If your router, such as the Swisscom Internet Box, supports the international DECT iq standard, registration should be technically possible in principle. In most cases, newer routers can be switched to "search mode" by pressing the DECT button, as is the case with the Fritzbox. However, I am not informed about Horizon, but I think that it does not support this yet.
Hopefully this will change.
Good luck.