1. Hi for this trick to be effective the attacker has to be in the same Paging area as victim.\
2. Moreover Paging area can be very huge. It can be several kilometers unlike what we see in Location Based services! When an incoming call comes the whole paging area would be paged so I think it would be unreliable unless Location Based Services can be tapped into (which I belive will be difficult).
3. Moreover as networks move to LTE & 3G things can become more complicated?