Writing for radio 7: how I wrote 'Calling'

Now that 'Calling' has been broadcast, and the flurry of flattering Facebook comments and tweets and emails had died down, I meant to do one last post in this Writing for Radio series: how it feels to have your story read on the radio. But then a friend who writes magazine fiction for a living started a discussion of where stories come from, and I realised that actually I haven't been able to talk properly about where 'Calling' came from, because it would have given away the story. So this...