Um - I think I saw a VOIP ready ADSL modem somewhere.
It includes a point in which to plug in a normal land line and then an out plug to plug in the normal POTS telephone line.
That's an example of connecting your land line to VOIP, and that will require a specific ADSL router/modem that has the VOIP hardware adaptor built in.
The usual ADSL router/modem does not even bother with these kinds of hardware connections, as they expect you to be doing VOIP solely on your PC.
So - if you want the ADSL modem/router that can do VOIP using a normal phone, then, check the modem/router carefully. Asking teklom if the router supports VOIP is a null and void question, because VOIP is an inherant part of any TCPIP network. You should ask if the ADSL modem/router can control VOIP access on your POTS (Plain old telephone system), that's more like the correct question to ask.
Gewd luck.