So, assume that there are two Galaxy S3 phones (i9300)s. One of em has a "No Service", "Baseband Unknown" problem while the other works like a charm. Both of them are rooted and flashed with custom ROMs. (CM11 and CM12).
So, if the phone with proper
/efs makes a nandroid backup of
/efs and then that backup is restored in the phone having issues, then this should technically work.
Question is, will it?