Question Author
Thanks for your answers. We have had Sky for some time but only seems to be recently that these calls have been occuring during our own phone calls. It almost seems that when we make a call it "wakes" the Sky box up - I get sick of apologising to the person I am calling. Of course having failed to make the connection the first time, the box tries again a few minutes later. as I keep an eye on my call charges, I know that the box is not making any calls that I am being charged for.
I believe that Sky use the telephone line to update the software in the box, so disconnecting it may prevent you from receiving the latest issues.