I've taken advantage of calling ahead also because of having purchases blocked in the past. One thing that can trigger a block (according to a CSR) is purchasing gasoline, then a large ticket item later or several purchases in a different city. I've also had the embarassing experience of purchasing gift cards at a grocery store, rather large amount -- spread over two transactions with the second one being denied even though the amounts were different... Nothing like getting stares from people in the line behind you while the cashier has to deactivate all the gift cards, etc.!!! I was told to try to advise ahead of time for purchases like that also...