I need the code to unlock my g1 - HTC G1

You have a few options:
1) There are several pay-unlocking services online, I think $20 is typical for a G1
2) You can call T-mobile who will give you the code after 4 months (I think) of having your contract with them
3) If you really want to do it yourself, for free, you need to replace the phone's bootloader with the one released with the development version of the G1. Full instructions are here: http://www.intomobile.com/2008/12/08/diy-hack-and-unlock-your-t-mobile-g1-into-an-android-dev-phone-1.html.

If you decide to replace the bootloader, you'll be able to install any version of the android operating system you like & the phone will stay hardware unlocked. You'll lose any t-mobile branding & their software tweaks - so make sure you keep a copy of mobile internet settings etc from the phone.

Hello,
Its easy to get you g1 unlocked, currently there is no free service or software to unlock g1 mobile. However you can get an unlock code from http://unlockg1mobile.com
they are in business for more then 2 years, prices are most reasonable and customer support is great. Got several G1 unlocked from them. Code comes in email and unlocking takes less then a minute.

You have to either enter you're google account information or hard or soft reset your phone.

http://cellphoneforums.net/htc-g1/t289074-how-do-hard-soft-reset-g1.html