There's never a policeman when you want one
I'm hoping that the DPP will order the police to take another look.
However, whilst we're waiting for the gears of politics and law to grind into action, I would like to point you at an excellent article on channel4.com/news which explained just how you might go about eavesdropping on a phone.
When this story first broke I was of the opinion "But I thought GSM was secure!". Then I thought "Ah, they've been hacking by means of default pins". Well, it seems the NotW peeps have been doing just that - but the article on the aforementioned site explains about that and several other methods besides.