Cordless Phone Ext and Modems?

Hi.
I've just come across these cordless phone extension kits where you plug one
end into the phone socket and the other end into a mains plug which is
thereby converted into a extra phone socket. Anyone used one of these in
conjunction with a modem? I'm just wondering how badly it will effect my
connection interms of speed; right now I'm getting about 48.0 kpbs. Thanks.

Fludge