Can the NFC hardware within Lumia 920 emulate a 125 kHz Proximity Access Card?
It looks like the NFC hardware implements the standard that is a superset of the standard that access cards use. But I don't have enough knowledge of those radio standards to understand if a phone can work only as a receiver or also as a transmitter of such signals.
I will also appreciate a link to a good overview article that explains those standards in simpler terms than the official specifications.
Currently, card emulation is not supported by the Windows Phone proximity API.
Sources:
It is impossible from the physics perspective and standards. NFC is based upon ISO 14443 and is using 13,56 MHz wave carrier - which is high-frequency layer - it is typically the electric field scope.
125 kHz is the proximity scope (125 kHz - 134 kHz) which uses magnetic induction (and magnetic field) as the communication environment.
Conclusion - it is physically impossible in this exact case. You could if you would use 13,56-solutions as proximity (this is possible).
Take a look here: This white paper details the features in Windows Phone 8.1 that you can use to create a UICC-based NFC card-emulation app.
http://www.microsoft.com/en-us/download/details.aspx?id=43681
来源：https://stackoverflow.com/questions/14124799/windows-phone-8-device-as-a-proximity-access-card