I did a search of this forum and didn't find this, so I am posting.
If it has been posted, please delete.
Found this searching the Internet.
It worked for me. After upgrading to 2.0.2 problem occurred.
Seems to be a common problem, judging from the number of posts, I found.

iPhone doesn't ring when it's in sleepmode

1.) Reset the phones network settings
2.) Reboot the phone
3.) Put the phone in airplane mode
4.) Reboot the phone
5.) Take the phone out of airplane mode
6.) reboot the phone.

To reboot the iphone hold down the sleep/wake button, and the home button at the same time for 6 seconds (until the apple logo appears).