*123*11# work on most phones, but on HTC phones you need to download a .cab file for this.
If you are on prepaid, phone 173 and ask to be put through to 1555 (tecch support) who will forward the settings to you, or if on contract, phone 808 and ask for 1555 (dialing 1555 directly will give you an error message saying that the number does not exist.)
It irritates me that leaf has a phone on their site by no settings like the HTC s740 at least have a manual list of the setting so you can try apply them yourself.