I'm sure that Apple lost many of the 3G iphone customers from the 4.0 update. Most iphone 3g users that I know complain about this problem for about some time now. I'm one of them. I even had to google a way back to 3.1.3 version of the iphone OS to have my cell phone back. Also we don't have an official way to go back to an older version and we have to "hack" a way through it with 3rd party solutions.
I hope ios 4.1 will fix the problem permanently and also I hope they improve their quality control at backwards compatibility for software that comes out from now on.