Telus Mobility has released a free Windows Mobile 6 upgrade for the HTC P4000. By updating your software, you will gain access to the new features of Window Mobile 6 along with additional improvements. The upgrade also fixes an issue where a random freezing issue could occur during normal operation, power up or power down.
Note: The upgrade will replace the current ROM image and will erase partnership and all user data and programs on your device. Be sure to back everything up before you start.
Source: PocketPC Thoughts