I've been thinking about using software to SMS message to a phone, and
requiring a reply to complete the logon.  I've also got a more
cryptographic method that I've been procrastinating on, but discussing
it at this stage would be premature.
--
http://www.lightconsulting.com/~travis/  -><-
"We already have enough fast, insecure systems." -- Schneier & Ferguson
GPG fingerprint: 50A1 15C5 A9DE 23B9 ED98 C93E 38E9 204A 94C2 641B