Don't use your Hala card, it'll cost about £20 for 5 mins! Skype(as everyone says)is the way to go. You can get a Skype-in number for not very much which means friends back home can call and just pay for a call to a UK landline (i.e. free if from a mobile with free mins).

Should anyone ever want to know, I'm an expert on cheap ways to call Qatar from the UK