Lost contact info with 4.2.1
I lost a bunch of my contacts when upgrading to iPhone 4.2.1 -- anybody else have the same problem? I didn't notice until later, when I went to call somebody and their phone number was gone. Then I went to email somebody else, and their email address was gone. It looks like it kept all the contact names, just deleted some info. 
Comments
I also just had this happen to me. Kept getting kicked out of my apps, so I turned my phone off and back on and realized I have lost all of my contacts. Not good!!! I have some that I only contact once in awhile during ball season, so I have no idea how to get iPhone contacts back.
Given iTunes' ability to automatically create backups, you can use a recent backup to restore iPhone contacts.
1. Open iTunes and connect your iPhone to your computer using the provided USB cable or your Wi-Fi connection. Wait until you see the iPhone icon appear in the left column of iTunes underneath the “Devices” category.
2. Select your iPhone and right-click it (Ctrl-click on a Mac) from the list of devices.
3. Select "Restore from Backup." ITunes displays your iPhone name as well as the most recent backup available. Click "Restore" to return your contacts to your iPhone.
4. Update your firmware, if necessary, as the backup does not include these updates.
Given iTunes' ability to automatically create backups, you can use a recent backup to restore your contacts.
1. Open iTunes and connect your iPhone to your computer using the provided USB cable or your Wi-Fi connection. Wait until you see the iPhone icon appear in the left column of iTunes underneath the “Devices” category.
2. Select your iPhone and right-click it (Ctrl-click on a Mac) from the list of devices.
3. Select "Restore from Backup." ITunes displays your iPhone name as well as the most recent backup available. Click "Restore" to return your contacts to your iPhone.
4. Update your firmware, if necessary, as the backup does not include these updates.