What apps/themes have you installed? At least one of them is not playing nice and causing your phone to boot into "safe" mode... your only fix is to find the culprit and remove it from your phone... It could be that you are trying to run an app/theme that is not intended for your current level of iOS... which is probable NOT 4.x... given the performance issues on the 3G iPhone for iOS 4.x
Like Hank said, it's just something you installed that's not compatible. Can you give us a list of what you've installed? And also your firmware version?
If you're on 4.3, although with a 3G I'm thinking that would be PAINFUL but if and you have infinidock that would be my first suspect. If you're on a lower firmware try disabling everything under Winterboard that is something else that directly uses the springboard. Those are my two top suspects but like these guys have said you just have to think about what you installed when it first started to happen.
I keep getting that message as well. I notice it only happens with biteSMS and only when I tap the numerical icon on my status bar indicating how many unread texts I have. I've downloaded CrashReporter, but not really sure what to do with that App.
I've experienced this problem too for the past week. I'm on a ip4 4.2.1 I'm guessing it has to do with the 5 icon dock tweak because every time I had to restart the springboard I had to re arrange my 5 icons back to where I had them before the springboard crash. Also, this crash only happens when my battery goes completely dead.
This is not really going to help you didn't give us any info other than you're on a 3G. You also didn't tell us if you've tried any of the things that have been suggested and whether they worked or not. So give us a little more info and maybe we can help you out.