I think he means to lock the phone, akin to pressing "alt-ctrl-delete" on your PC and lock the PC so that nobody else can use it. Since the phones don't support this functionality, the only way you can get this to work is using EM.. the user has to log out.. and that effectively stops anyone else from using his profile. The drawback is that calls will directly overflow, but then again if you lock your phone, you're probably not around to unlock and answer calls anyway.