Call a few shops and ask for Cordless VOIP phones, Tell them you have a router that ha VOIP Wifi capability's.
Or if you are interrested in a total VOIP Solution for your home phone (basically u don't wanna make call on normal telkom phone prices)
Its also a solution that uses your current ADSL line, with a special phone that runs on data. (meaning it doesn't make a call, it simply uses data)
Its Very cheap.
You can get any wireless dual dect phones.
So the you can plug the "base station" into the router and then just setup the second phone anywhere else in the house.