@otc11 

Well, I have no answers but I do have an iPhone 12 Pro Max, an Archer A20, and my ISP is T-Mobile.

What you are experiencing is quite similar to the problem I had with my ISP, Router, T-Mobile and my prior LG G7 Android phone.

I also do NOT use Smart Connect either. Also, one bar or less in the home.

When I got the iPhone a few months ago, connecting and using the Internet on it was no problem at all. Making a CALL, rarely went through. I'd call my wife's phone, NEVER rang. She'd call me, got voice mail. Occasionally if I rebooted the phone, it would work immediately but a short time later, problem returned.

Called T-Mobile. Phone agent couldn't call my phone either. They decided I should either switch on and off Airplane mode and that might fix it, nope. Same way, works for a short time then fails. So they said they'd send me an indoor booster. Never got it... called again and this time, a different agent. She tried the same stuff and no better. Asked me to forget the network and reconnect. Even trying all 3 bands. Then she noticed my SIM card was the same I had before. When I got the iPhone, it did come with a SIM card. Store said they'd use the one from the LG, easier to do. Worked fine, but not on home network? She asked if I had the SIM, which I did. Gave her the number, she told me to turn off the phone, put it in, and wait 5 minutes after I do this, as she'll update my account with the new SIM, and then turn the phone on. She'll call me in 10 minutes. NO PROBLEMS since then.

Long story, but all I can say it isn't the router.

If you got the phone new and didn't use the SIM that came with it, maybe you should? I'd also not use SMART CONNECT and have the iPhone connect to the 5-2 SSID all the time.

Good luck.

@IrvSp Thanks!

The SIM is the one that came with the phone, and I tried turning off Smart Connect, didn't make a difference.

As far as I can tell, once WiFi calling is active it stays on, it's just rejoining the network that makes it iffy. Seems to work perfectly once "Xm WiFi" shows.

Might still give another router a try.

@otc11 

Was the phone properly 'conditioned' when the new phone was connected? Check with the Cell company.

@IrvSp What does that mean? It was purchased through the carrier's store....

@otc11 

I'm just suggesting and asking the phone support. In my case, the OLD SIM was taken out of the old cell and put in the new phone. If this was done for you it could cause problems. Also, the phone Co. store phone might have had a SIM in it that would work, but your ACCOUNT had to be updated too. Just see if it was, that is all I was saying. I did check my account after the phone was purchased and they did show the phone as on my account. There still needs to be a configuration change if you had an old phone.

Bottom line, my Archer A20 workd fine with an iPhone 12. Since I did have a problem when I first got it, and T-Mobile was able to 'fix' it, it is not the router.

Well for anyone curious, the last 3 days WiFi calling has worked fairly flawlessly. I did 2 things:

-Set up port forwarding/triggering for 500 and 4500 on the router

-Took out the SIM card, turned off the phone for a couple minutes, popped it back in, turned it back on

Since doing that Friday afternoon I've left and rejoined my home network dozens of times and WiFi calling shows up right away.

otc11 wrote

-Set up port forwarding/triggering for 500 and 4500 on the router

@otc11 

Are you using a VPN? IPSEC?

https://learningnetwork.cisco.com/s/question/0D53i00000KsumeCAB/why-do-we-use-port-no-udp-port-500-and-udp-port-4500-in-ipsec-vpn

I don't have any ports forwarded and it works fine on my iPhone 12?

More than likely it was the SIM that needed to be reseated or re-initialized.

@IrvSp I'm not, so I think you're right. Still don't understand why the issue was unique to my home network, but if it works it works.