what kind of IP phone is it!!! if its a skype IP phone, just download the software and make calls….! find out what kind of VoIP (SIP) provider of this phone!!!

you can not just plug it in the computer, you gotta download the right software….!

I use several VoIP and SIP providers and free services!!!

For Security reasons, the IP address needs to be registered at the Server, so nobody can steal your phone and act as though its you.

There are many unanswered variables to your question.
It always helps to know the make and model of the IP Phone.
And, who do you currently have VoIP home phone service with?

If you did not self-administer your home phone VoIP account with BYOD (bring your own device), then you probably have a “pre-configured” ATA adapter supplied from your VoIP service provider and it is locked.
If it is a locked box they provided you with, then their service is probably locked to – meaning you cannot just connect any ATA (or IP-Phone) of your choice to their service (that’s where BYOD services are useful).

And, is the IP-Phone you brought home preconfigured with another service, or is it already configured for the VoIP service you have at home?