My VoIP is via a Thomson Speedtouch 716 ADSL router which I got free...yes, FREE from Digidave.co.uk. Offer looks as though it's still open and now wifi as well! See:
Digidave.co.uk
My ISP is VM Cable. The cable comes in from the modem and my analogue (but not for long) phone plugs in, as can the landline phone line if you want both available.
Setting up is a bit fiddly - I edited the massive 'user.ini' file to get mine going but Digidave are helpful. My VoIP provider is sipgate who also provided a separate home-town phone number as well as cheap calls and good service.
Hope that helps.