Phone lock

From TreoCentral

The Treo 600 and later models allow you to lock the Treo, preventing unauthorized users from making voice or data calls. This is done through the phone lock option on the options menu in the phone application. To use your Treo to make voice calls, you would have to enter a pin number correctly.

The Treo comes with an application called Security that will password protect your Treo, but this method does not encrypt your data. There are many third party programs (such as mSafe) that allow you to lock or encrypt the entire contents via a password or pin number.