Is there such a service? I don't mean a cell phone, but a unit you plug in to the wall and plug your cordless, corded phone into.
Not that I know of but IP Phones -- These specialized phones look just like normal phones with a handset, cradle and buttons. But instead of having the standard RJ-11 phone connectors, IP phones have an RJ-45 Ethernet connector. IP phones connect directly to your router and have all the hardware and software necessary right onboard to handle the IP call.