Alerting admins when certain fields are changed via profile & checksum?
If you have hosting that allows you to turn on Detailed Logging, there are two extensions that provide address history.  One is in Extended Reports; the other is Joseph Lacey's Address Log report.  It should be relatively simple to extend either one to support phone/email/etc.

Another option, low-tech but effective, would be to export the contact details ahead of time, then export again after folks have filled things out.  Paste the two spreadsheets into one and use a simple formula.  E.g. if old email is in column C and new email in column H, =IF(C1 != H1, "Changed", "") in a new column will label any records where the email changed.