As far as I know there is some confusion among customers here and on howardforums.com as to what constitutes "use". It has been suggested that storing and retrieving voice mail or sending a text message to the number might count as activity. If this is the case your periodic checking of voice mail may reset the clock. I would love to know the answer to this actually. I tend to get to the UK in clusters. Lots of trips in a short period then none for several months and would like to know in detail the parameters on keeping the numbers.