Have a comcast cable modem and want to have VOIP?

I know I can use headset (mic.+speaker) but I want to have better quality and I want to avoid paying monthly rent to comcast for its Motorola cable modem, am also using trendnet wireless router and I want to know if is there any device which can serve all my purpose for example 1.cable modem 2.wireless modem 3.voip?

Related posts:

1. Will there be a problem if I connect the VOIP adapter to my cable modem instead of my wireless router?
2. How do I set up a wireless router with voip?
3. Comcast Cable TV Special Deals
4. Current Comcast Cable TV Special Deal
5. Can I use my laptop to distribute my broadband to a voip router through the ethernet port?