Custom Filed – Autonumber

Hi,

I’m looking for the plugin like yours, but I have the strange request.
I have requirements to list users anonymously by their numbers and allow other users to contact each other with private message ( another plugin )
So I need the custom field that will assign the number to the user ( not the default WP User ID ) and this filed can be listed anywhere else on post or blogs instead of username – so all the users of the website can see only the number of the other users and no personal information. Or I’m talking nuts here???

Regards,
Kos