We have a number of user's in our company who are using iPhones that have been provided by our company.
How can I remotely wipe out all data on an iPhone owned by our company?
For iOS 5 Apple now provide the Find My iPhone app that allows you to (amongst other things) remotely lock and wipe your idevice.
Exchange in brief:
Log into your exchange webmail, go to options -> mobile devices. Select your device and then check Wipe All Data from Device and cofirm.
The next time your device connects to exchange it will be wiped.
If you're using exchange look here.
Do you use a Microsoft Exchange Server? Iphones connected to such a server can be remotly disabled or wiped. You could also search the App-Store for an Anti-Theft software like F-Secure Anti-Theft