The backup sqlite db file is located ~/Library/Application Support/MobileSync/Backup/<phone ID>
and is named 3d0d7e5fb2ce288813306e4d4636395e047a3d28
.
It's name is an SHA1 hash of the full path of the file on the phone, plus its Domain.
$ printf 'HomeDomain-Library/SMS/sms.db' | openssl sha1
3d0d7e5fb2ce288813306e4d4636395e047a3d28