@McMoo
It may be reasonable for Vodafone to keep billing and invoice information for seven years due to UK tax laws, but they certainly don't need my date of birth or email address.
I'll (almost) leave the final word on this to the ICO who enforce the Data Protection Act "...there is a significant difference between permanently deleting a record and archiving it. If a record is archived or stored offline, this should reduce its availability and the risk of misuse or mistake". Such as serving it up to all and sundry via a faulty website, for example.