I got it to work! Thanks very much to help from the xda developers forums.
http://forum.xda-developers.com/showthread.php?t=2434226
Can we put S3 S-voice on S4?
I downloaded the latest S3 software to my computer and unzipped it. Looked in the system folder - apps folder - voicetalk.apk. That is the S3 S-voice apk.
Copied that to my SD card.
Using Root Explorer, I renamed the native S-voice app (it's under Root - System - App) to .bak instead of .apk.
I then copied the file from the SD card to the App folder. Changed the permissions to match everything else (rw-r-r).
Rebooted - and voila! S3 version of S-voice installed.
S voice now recognizes all my contacts again.
I made some mistakes getting to the above. At some point, I also actually ran the installer for the S voice apk through root explorer...I'm not sure whether that is needed or not. So if the above doesn't work, then actually run the installer and reboot.
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