So ideally a handset device capable of recieving and making calls to a limited number of devices.

When you say a “limited number of devices” do you mean a closed system when you have provisioned all the devices or do you mean you also need to be able to receive calls from standard phones?

To replace a landline you can just use a service like Vonage Home for about $10/month. If you want to setup your own PBX (phone system) for calling your own managed set of devices, then you need more. In any case, you always need a SIP service if you want to make and receive calls with regular phone numbers.