VOIP Phone Equipment with Comcast Voice?

I spoke with someone that has English as a second language that didn't knopw the difference between an RJ11 and an RJ45 plug, and didn't really understand the difference between an analog device and a VOIP device.  Maybe someone here knows the answer to my question:

Can I use a VOIP phone on my Comcast Internet connection or do I need to transfer my phone number to a VOIP company like RingCentral?

Specifically, I'm looking at a Polycom VVX 150 to replace a very old Panasonic 2-line phone in my home office.