Modem dual band with voIP?

Solution
There is not a lot of selection. Many of these devices are not actually VoIP depending on the modem type. A cable modem many times has a special voice over cable. It is VoIP but it is special and only connects to the cable ISP. Many ports on DSL modems are not actually VoIP they are analog ports that just connect though.

There are not many devices that have actual VoIP. It makes it even harder when you need some form of modem in the box.

I would use a external adapter, at the moment I forget the cheap one I used, but something like magicjack. You could then buy any modem/router your liked
There is not a lot of selection. Many of these devices are not actually VoIP depending on the modem type. A cable modem many times has a special voice over cable. It is VoIP but it is special and only connects to the cable ISP. Many ports on DSL modems are not actually VoIP they are analog ports that just connect though.

There are not many devices that have actual VoIP. It makes it even harder when you need some form of modem in the box.

I would use a external adapter, at the moment I forget the cheap one I used, but something like magicjack. You could then buy any modem/router your liked
 
Solution

Which are cheap and good voip adapters?
 
Its been so long since I used a VoIP adapter I forget, and I went and looked in my junk box and didn't find the one I have. I have been using google voice and google hangouts on a cell phone. Google voice though is not VoIP it is something else so I don't know if hard wire phone can be connected to it. Still free compared to a monthly fee made me decide it was ok to not use a physical land line phone.

The VoIP service you use should have a list of adapters that work well with their system. Almost all are SIP based VoIP.
 

What is a SIP?