hi mate r u on the old boot rom or the new as it makes a difference
here`s how u can tell
HERE`S HOW TO TELL IF OLD OR NEW BOOT ROM ON THE IPHONE/IPOD TOUCH
The serial number is one way to check; if the 3rd, 4th, and 5th digits of the number are 940 or higher it more than likely has the new bootrom. If it is 939 or less you should have the old bootrom; there may be some iPhones that don't fit into that criteria so here is how to check the bootrom and know for sure what you have (no jailbreak is required):
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.
if your on the old boot rom u can jailbreak , or if your shsh is stored on cyidia then u can downgrade to 3.1.2 then jailbreak through blackra1n but iphones with new boot rom will be theared [meaning if u let the batterey die you will need to blackra1n again 30 secs it takes , geo hot and the dev team are waiting for the new fw 4.00 to be released before theyy make any new major jailbreaks for new boot rom 3gs iphones , give us a shout if u want me to take u through it mate