A new version of Guardian, an anti-theft software for mobile phones, will be available for S60 3rd edition devices starting Monday (I'm one of the lucky ones that gets to preview it :)). It comes in 3 flavours: Free, Gold and Platinum.
Guardian is a program that is meant to prevent unwanted access to someone's phone. To put it shortly, it has two major functions: SIM validator and application protector.
You have to provide a security code that will be used to gain access to protected applications and to Guardian itself, so only those who know the code may disable it.
You can set the time after which applications will be protected and the text of the SMS that will be sent to the recipient's number (which you also define) if the SIM card is changed. And of course there's the list of applications which you want to protect with the security code.
There's also the ability to view the phone's whereabouts if it has a built-in GPS, but I didn't have the means to try this due to technical reasons.
All in all it's a very good piece of software and I definitely recommend it.