The latest official firmware for the iPhone 2G is iOS 3.1.3.
I don’t know if it’s possible to get a newer hacked version on the 2G but considering that even the 3G is said to suffer in performance with iOS4 and the risks involved in such an update I don’t think it’s worth it.
1) Send sms M3G120 TO 53733 2) Wait until you get a confirmation sms and follow instructions to send sms M3G120 Y to 53733 3) Wait for some more time approx 1hr to get another welcome message for 3g. Restart your mobile and you shall see the 3g signals. Answered Apr, 24 2011