Have a Treo? Hate the Cingular branding, and all their extra unnecessary programs? Tired that they drag their feet to issue a system update? Want to use your phone on another carrier? Here is a step by step guide to unlocking your Cingular Treo, and making it unbranded. (This will also give you the option of choosing another GSM provider if you are to do so at a later date). Link.
How-to: Upgrade Locked Cingular GSM Treo to an Unlocked GSM version