Plenty of people around the world by now know of the allegations of philandering made against the English footballer David Beckham, based on claims made to the media, and also on transcripts of SMS phone messages that are said to have been sent between Beckham and one Rebecca Loos.

The ins and outs of the affair are none of our concern, but what did concern me was this explainatory article in The Advertiser:

He apparently even has offered to produce his mobile phone records to prove his innocence. It may surprise some mobile phone users that some carriers retain details of text messages.

In Australia, Telstra keeps SMS messages for up to 28 days and Optus keeps theirs for three days.

I have three questions here. First, why are telephone companies keeping records of these things at all, and second, why is there such a large difference between Telstra, the dominant company that is still half owned by the government, and Optus (which is now owned by Singtel, the phone arm of the Singaporean government.) And thirdly, why are these messages apparently so insecure?