Greenpois0n and Limera1n do the same thing since it's the same exploit (Geohot's). This exploit uses another (by Comex) to untether it. It is that exploit that doesn't support 2g mc. Greenpois0n was originally going to work with another exploit, SHAtter, and that only supported newer models, such as iPad, iPhone 4 and iPod touch 4. As soon as either of the jailbreaks change exploits to untether it, 2g mc model will be supported.