Fingerprint scanners have been available on a few WIndows Mobile devices since at least 2003/2004 (perhaps earlier). The HP iPAQ h5550, for example, was introduced around this period with a fingerprint scanner. Such biometric components have not caught on in the intervening years. One possibility is that it is probably inconvenient to take off a glove (in cold environments) just to unlock a PDA or phone.
Originally posted as a comment by Todd Ogasawara on mediabistro.com: MobileDevicesToday using Disqus.