To make it clear, I do not condone phone hacking. I condemn it.
I just think this might be an exceptional case. I agree the journalists should have pointed out their thinking (which they claim as their reasoning in the article cited on page 1) to the police, who are less likely to have encountered the full mobile problem in their working lives.
I hope the police would have already thought along those lines, though.
AFAICS there is no reason to lose any information in a mobile text message, provided you write down the text of the text and the details of the text on a piece of paper or into a computer before you delete it.