Can they not pay for their own calls?

I suppose that we'll never know. Some might argue that we should not be entitled to know. But that can be discounted as we taxpayers paid for the call. The Times reports:

Details of private phone calls from Gordon Brown’s Scottish home, including a call of 2 hours 42 minutes call to a mystery address in Canterbury, were made public yesterday.
The time, length and geographical destination of 21 calls were disclosed when the BT bills submitted as part of his expense claims were published by the House of Commons. The numbers were blacked out.

Who was he phoning in Canterbury? And what did it have to do with his parliamentary duties? He has a fixed telephone link from his constituency home to 10 Downing Street so it is unlikely to have been on government business. Or could it - just possibly - have been Mrs Brown?