ChevronWP7 Unlocker & Cert download - *here* + video tutorial
As people may know, Chevron have removed their unlocker download for WP7

so I thought I'd archive it and make it available for everyone here still:
http://www.megaupload.com/?d=JY0ZFVKD
EDIT: Thanks to
Cendaryn we also have the required security certificate

- the easiest way (thanks to
Talys) to install the cert and unlock your WP7 is to do as follows:
1. Unzip file, and attach chevronwp7.cer (see below for file) to an e-mail to yourself
2. Open email in WP7
3. Tap attachment once, turns it into a shield, tap it again, goes to install certificate screen with white letters on black screen
4. Click install at the bottom
5. Make sure registry is modified:
Code:
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\WindowsPhone\ProxyPorts]“DeviceReg”=dword:000069C5
I think the WP7 developer tools from MS does this, but you can add it in manually (it's a 32bit DWORD)
6. Plug in phone and leave Zune running
7. Run chevronwp7.exe, click both checkboxes
8. Click unlock
Excellent video tutorial
here thanks to
Jaxbot
[Edit 8th Dec 2010]
Worried that Microsoft has relocked your phone? They haven't, look
here
[Edit 20th January 2011]
Want to keep your unlocked HTC from re-locking every sync? See
here
Hope this helps someone.