I like to confirm that Custom 2.2Firmware (which was created with pwnage2.2.1) is perfectly running on my iphone2G with fake imei. So all mails regarding to 2.1Custom FW would be upgrade their iphone to 2.2. I created a new 2.2firmware with Cydia and Installer in it, so you can able to restore your phones to this firmware. If you still in 1.1.4FW, you can again follow my tutorial and just you should use 2.2FW instead of 2.1FW. Anyone who already use 2.1FW with fake imei can safely restore your phone with 2.2 Custom Firmware.
Baseband is the same so you do not need any bootneuter operation to unlock. If you have chance to create your own 2.2FW, you shouldnt be select bootneuter and thats all. You can safely restore it.
By the way, due to the itunes, you should restore your iphone. You will have error when you try to upgrade. You can switch your iphone to recovery or DFU mode.
I decide to create a blog to help others. I'm getting hundreds of emails and you can know easily that it is too hard to reply all of them, but I did!. So, I will share my custom 2.2FW within my blog and to whom written in this threat and also mailed to me will have a new link to have 2.2 Custom FW.
For new people, I will also send them 2.1FW links to have practise to get ready to 2.2FW.
Greetings from Turkey,
P.S. 2.2FW is awesome.. I have also iphone3G..both of them are very stable and fast now. I really like it. Thanks apple to fix most of the major bugs.