What application? Encryption for e-mail, general encryption for data, VPN/SSL or all? In other words, what are the business requirements, and what is the risk you want to mitigate?
I've liked F-secure products. They don't have crypto for what I have (a Palm Computer), but they do for Pocket PC.
If you are interested in just a secure store for sensitive info, there are shareware products (search on www.palm.com). I use Secret! for that.
There is a version of PGP for PalmOS, but it does not look automated.
For more information on this topic, visit these other SearchSecurity resources:
Best Web Links: Encryption
Executive Security Briefing: Are PDAs backdoor security threats?
Tech Tip: Thinking about wireless security
This was first published in June 2002