For those having Wi-Fi calling issues lonie23 actually talked to Samsung and this is what they had them do and it seems to have solved the problem. This is the second post I have seen with the same instructions from Samsung to solve KitKat issues on the S4 and Note 3. Sounds like something in the update doesn't clear or write over the cache so get some garbage in the cache causing a problem.
okay guys! I got you the fix from Samsung and it worked immediately with my phone! So if you're having issues with wifi calls after the update this is what you do to fix it:
You need to perform wipe cache partition on the phone
1. Power the device off (remove and re-insert the battery).
2. Press and hold the Volume Up key and the Home key, then press and hold the Power key.
3. When the device vibrates; release only the Power key.
4. When the Android system recovery menu displays; release the Volume Up and the Home key.
5. Navigate with the Volume keys to the wipe cache partition option and press the Power key to select.
6. After user cache deletes, press the Power key to reboot system now.
And there you go! That should fix it