So I took a clue from Oakdale Dude's comment of his phone taking 2-3 minutes to re-enable WiFi calling and conducted a few experiments. I turned the WiFi and WiFi calling off, turned my phone off and restarted my phone outside where I knew it would get T Mobile signal. After a few minutes I went back inside my house, turned WiFi on, let it find and connect to my WiFi network and then turned WiFi calling on and waited. The WiFi calling tile started blue, went red (REG 99 error) went blue again, went red again (same error code), went blue again, then at about the 4:00 minute mark, it went green and enabled WiFi calling. I had never waited that long, so I had never seen it connect without going through the "airplane" mode routine. Then, I tried to the same experiment with my wife's phone. It enabled WiFi calling in appox. 17 sec! She has never been able to get WiFi calling without toggling "airplane" mode on and off. And she was much more patient than me. Strange how it is all of sudden working. I had a conversation with T Mobile yesterday and today the WiFi calling enables automatically. I'm generally not a conspiracy theorist, but today during these experiments I also noticed I have cell signal in my house, not strong, but since we had no cell signal inside, much better than it has been since I switched to T Mobile.
Anyway, to wrap things up, I left my WiFi signal today for an hour or so, came back and although it took close to 5 minutes, the WiFi calling "automatically" enabled. My wife's phone took about the same amount of time also. I always assumed that the enabling of the WiFi calling would be much quicker than 4-5 minutes. I guess this is a lesson learned. Thanks for all the help.