Replace Key Cards With RFID

If everyone in a company office is carrying a smartphone with RFID, why have traditional key card readers?  Replace those readers (or add an RFID module to the readers) so it reads the smartphone RFID.

The benefit to the employee is one less thing to misplace.  The benefit to the company is one less physical thing to issue.  The physical security system would interface with the RFID replaces, just as they interface with the keycard devices.

For employees who want to implement this themselves, they could glue the keycard to the back of their phone.