Other than those capabilities that require you to be subscribed to a carrier's service, sure. I have 2 phones that are currently connected to carriers - and about 10 that aren't, that I still use for various things.
(BTW, ANY cellphone in the US MUST be capable of calling 911 - whether it's connected to a carrier's service or not. So a charged, but not connected, phone in your car is a good safety measure. Just keep it charged.)