Just when parents thought Justin Bieber couldn't possible gain any more influence over their teen daughters, it was announced that the superstar is encouraging them to spend more of their parents' cash with a new prepaid debit card.  Bieber has signed a deal with BillMyParents to endorse it's teen-focused SpendSmart prepaid card.  The New York Times reports that the average age of a SpendSmart card user is 16.  It has a monthly fee of $3.95.   There are also ATM fees, and a charge if the card is inactive for 90 days.  That all adds up to "parents beware."