Which modem to use for DSL internet service?

[kkfng]

Which modem should be used for dry loop DSL and cable correspondingly?
It would be great if I can get suggestions for both modem/router and devices that purely provide the modem functionality. Can a modem/router be used as just a router in case I change the internet service type? A pure modem can only be used for the DSL service? Thanks!

I am using the service from http://teksavvy.com/en/res-internet.asp

 

[VirtualLarry]

I am not aware of anyone that makes a device that is a DSL modem, and a cable modem, at the same time.