Fix iTunes: An unknown error occurred (1651)
By If you have iPhone 4 CDMA version, you may see the alert “iTunes could not check for an update to the carrier settings for your iPhone. An unknown error occurred (1651)” if you are using iTunes 10.1.1 or earlier.
To fix for this error, simply install iTunes 10.1.2 or the latest version of iTunes, because iTunes 10.1.2 or later has been updated to be compatible with iPhone 4 Verizon CDMA.
CDMA 
