iPhone 3G Tip:
If you use your Headphone jack you may experiance your iPhone no longer making those cool little sounds like New Mail and SMS ect. The Phone ringer still worked but everything else stopped working.
So far I have been baffled by the lack of info on the issue but if you power down your iPhone and power it back up using the sleep button your sounds will come back.
There are other people that have also been able to restore these sounds by inserting the headphones into the jack and removing them.
Edit: I am also seeing this if you do not fully eject your iPhone from iTunes…The same fix works