I would only use "Pro" handsets with the N510 IP Pro. Certain older non-"Pro" models such as the C610H, SL400 run without restrictions, but this is not currently documented anywhere. The more modern consumer handsets are probably intentionally neutered in functionality if you want to use them with "Pro" base stations. Details on interoperability with non-"Pro" handsets can be found here:

https://teamwork.gigaset.com/gigawiki...

The CL660HX works on the N510 IP Pro only with considerable limitations - even simple functions such as the call list do not work. I have tried it and cannot recommend this combination: You can't even make a callback to a missed or accepted call without re-entering the number manually.