Sherif Hashem which is a big iPhone hacker and developer and already worked with Dev Team and helped them in crashing Ultrasn0w 0.93, Has posted a video on Youtube showing how to Active iPhone 3GS / 3G and even iPhone 4 without having Original SIM to which the phone is locked. But in iPhone 4 you will need to cut the SIM Card, Check the video after the Jump..
Here's the video: