You can buy a device that transmits your phone signal through tour electricity sockets and by moving the reciever you can have a phone ext. in any room without wiring. Alternatively just buy a wireless phone with extra handsets.
Any electrician can do this. However, if it's just phone you need it's a lot simpler just to get a DECT phone - for example, see
Although we wired our house for phone extensions, we haven't used it for ages now since we did this. I think a pair of DECT phones (one base station, one charger for the 2nd phone and 2 phones) is less than €100 now. You can also get 4 phone setups. Probably cheaper than getting the wiring done, and definitely more convenient.
we have that arrangement on our office..... 1 base station, 2 nos. (1 phone + 1 fax). and 4 phones....... can use the two numbers simultaneously... dont know what the standing charges and usual bill is though....