Is there an untethered Jailbreak for Iphone 3gs iOS 4.2.1 baseband 05.15.04?

the newest version of redsnow is untethered but it's a unstable beta version. also in order to use you must need some files of ios4.3 which is only available for developers. as i know there is no free software for 4.2.1 untethered jailbreak. but there are many paid versions available. you may find them on google. i used a href="http://bit.ly/coMhz4" rel="nofollow"http://bit.ly/coMhz4/a for my 3gs and it worked for me but it's not free.