I have an IPhone 3GS with 4.2.1 firmware never been jailbroken. It has a new bootrom and 05.15.04 baseband. I do not want 6.15 baseband but I do not care if the jb is tethered or untethered. I want to use my AT&T network on my computer with the iPhone and I heard this was possible only after jailbraking. Is it and how would I do this on a pc?