I'm in no rush on my iphone as I have a BlackBerry. I will wait for the official unlock for 5.15.4. I don't like the idea of not being able to go back to Iphone baseband.
Well if you have an iPhone 3g with a specific bootloader you can use fuzzyband to downgrade baseband, but keep in mind that fuzzy band only works on SOME iPhone 3G. If you have an iPhone 3G download fuzzyband from cydia and open fuzzyband once its on your springboard it will tell you whether or not it will work with your device.