I'm looking into jailbreaking and possibly unlocking my iPhone 3GS and I'm reading all the instructions, but I don't seem to understand one little blurb about "old" and "new" bootroms.

Can somebody tell me what bootrom is considered "new" and what is now considered "old"?

My iPhone 3GS is currently running iOS4 Gold Master with Modem Firmware 05.13.04, the model number begins with an MB and the fourth and fifth digits of my Serial Number are 48.

I hope this information helps in any way, thanks a lot.