Yeah, that's what I did, but I saw on redsn0w's blog that you can apply the redsn0w update to 3GS with 6.15 BB in order to prevent GPS from crashing network services, so I thought there must be a way to use it while preserving BB...
For iPhone3GS owners with the 06.15 baseband, this redsn0w eliminates the network crash you saw when using Location Services in iOS5 (in fact, you donít even need to disable Location Services anymore during the initial setup). The cosmetic fix is to the visual countdown you see when going into DFU mode.
Itís okay to re-run this redsn0w over an existing device jailbroken at iOS5. Just choose ďJailbreakĒ again and de-select Cydia (in other words, all the checkboxes will be unchecked). If you are lucky enough to have an old-bootrom iPhone3GS, please pre-select the IPSW first (redsn0w canít yet auto-detect the FW version of your old-bootrom 3GS if itís already been jailbroken).