If you can check your iPhone and iPod Touch jailbreak info using F0recast, well you can also check whether your iPhone 3GS has an old or new Bootrom using iDetector.
iDetector is a simple and small utility developed by iH8sn0w (who are also behind SnOwbreeze) which will determine your iPhone 3GS’ bootrom.
Before you can jailbreak your iPhone 3GS, you need to make sure first that it has the older bootrom, as it’s the jail-breakable version as of the moment.
To use iDetector, you need to set your iPhone in DFU Mode. To do that, check out the video below.