If you are only going to talk to each other then you might aswell setup an account with voipfone.co.uk or (FWD) freeworlddialup.com and use a free softphone with a mic & speakers or headset, and you can use a webcam too. VOIP to VOIP with both these providers are free. voipfone however also allow calls to standard phones really cheap, atm FWD don't.
If you want to use the USB handset I got the skype* one from pcworld (which is usrobotics kit same as tesco I think) , ran a piece of software downloaded from the net and the handset controls my x-lite softphone but feels like using a normal phone.
Edit: *Ordered from the website and collected instore £13.99