The Register reports that a new type of spyware is under developmet for Windows based phones.

FlexSpy can be installed with out a user knowing it, and it will not show up any where in the phone's software. It can record information about an individual's mobile phone calls and SMS messages before sending them to a remote server allowing the user who installed the software to spy on the owner of the phone.

http://www.theregister.com/2006/03/30/flexispy/

I hope the Treo 700w has some software to lock the phone so others can't install this software!