VOIP phone to receive and make calls.

You need a SIP provider.  The SIP provider will be your old school telco and send the sip traffic to your ip address. you would then forward these to the ip address of your phone.

This phone is transferable to sip. But you will need a tftp server running to provide the configuration. Even nog all functions on the phone are supported in this sip mode. I would advice to look for a cisco spa 5xx series of yealink or any other modern sip phone.

If you're up to it, follow the step described here (soooooooo many pitfalls though for non IT ppl, you probably can't even get the correct files, as you need to be registered with Cisco):
https://www.cisco.com/c/en/us/support/docs/collaboration-endpoints/unified-ip-phone-7900-series/5455-handset-to-sip.html#sccptosip2

If you want to use it as a VOIP phone, for many VOIP cloud based providers, they don't care where the phone is connected.  I have clients with cloud based voip phones in their office   and they simply take them home to plug into their home networks (with Internet access) to work from home.  They work as if they were connected in the office.  They can Call, answer, transfer forward etc.

that is common this days, but dont try to use this kind of phones. a normal sip phone. that has no need to provisioning