Here to tell you How to check out your iphone 3G & 3Gs Boot Rom
(for possible to Downgrade or upgrade your iphone to get it unlock)

To check iPhone 3G/3GS bootrom version:

To check iBoot Rom Version on Windows
1. Put your phone into DFU mode (hold power/home till it shuts down and release power when display goes off/continue holding home till you hear a sound on your computer)
2. device manager > universal serial bus controllers > apple mobile device
3. Right click on this and go to properties
4. Click details tab and should be in one of the fields below (change the drop down box till you find iBoot information).

On a Mac:
Put the iPhone in DFU mode then navigate to "About this Mac". From there go to "More Info...", and select USB on the list on the left. Under the USB menu you can select "Apple Mobile Device (DFU Mode)" and that will bring up information about the iPhone. About half way down it will have the iBoot information: It will either be [iBoot-359.3] or [iBoot-359.3.2] (the 359.3.2 is the new currently unjailbreakable one). To get it out of DFU mode just hold both the home and power button until it powers back on.

for the Old Bootrom now still possible to get it unlock and jailbreak