You can use any DECT handset that is GAP compatible. I had an old set of three BT handsets that I was able to pair without any problems, turning them into VoIP handsets.

If handsets are not matched to the base station then you tend only to get basic functions e.g. making a call. Sounds like there are Fritz handsets so that it good.

Ive been looing into the the range recently as I need to extend things and as well as handsets I discovered that Fritz also do wi-fi range extenders.

I forgot to mention VOIP currently my 7390 is supporting an landline and a single VOIP number on the system. larter this year I will be adding a second VOIP number.

If you set it up properly, the Fritzbox is very versatile.

Another nice feature of the Fritz!Box is that you can instead connect the old DECT base station to a FON port, allowing all the handsets to be used for VoIP and landline calls without re-pairing them. And you still get caller-id, whether it's a landline or VoIP call.

It's a great piece of kit. I have three of them

I use one of these. The FritzBox connects to VOIP servers and also to the copper phone line (though mine is not actually plugged in). It handles POTS and VOIP as well as fax.

It can have up to five voicemail boxes set up.

On the local side, it has four phone sockets and works as a base station for several DECT handsets. I'm not sure how many: more than I have