Microcell Deregistered. Why can’t I reregister it?

The SIM card is an interesting possibility.

If you have very old SIM cards that have you have moved from phone to phone for several years, and was originally in an iPhone 5S or 5c, it would be the correct size, but it would not be provisioned for Wi-Fi calling. 

But that would be rather strange. Most people get a new SIM card every time they get a new phone...

Our phones came with new cards. And worked with the Mcell for months. Mcell deactivated somehow. Won’t allow me to reregister. And gives error needs new SIM card. Idk. 

Hmmm..   One has nothing to do with the other.

Unless At&t drew same conclusion.

Mcell had to shut down anyway, no later than 2/ 2022, when 3g shuts down.  

   WiFi calling is not working.   It's a phone feature that works on all iPhone.  One phone would be a defect.  All phones?  

I started reading through the forums (about the issue we’ve been discussing, not the SIM issue I inquired about). Apparently this is happening a lot. While one isn’t supposed to have anything to do with the other, it’s proving otherwise with some people. For whatever reason. I don’t pretend to understand why it’s happening. But it’s happening. And it totally blows. Rant over. :-/

I get you're frustrated.  But the Mcell has been on its way out since 2017 when At&t stopped restocking it, or selling it.  And because every phone they sold had wifi calling built in.

Since wifi calling isn't working correctly,  troubleshooting with Apple would be next.  Then warranty replacement.  If that fails, you have to switch carriers.

Since wifi calling isn't working correctly,  troubleshooting with Apple would be next

Before going to that step, there are a couple of things you can do yourself. First, try putting your phone into airplane mode and then turning WiFi back on. It is possible you have just a strong enough cellular signal to prevent your phone from connecting to WiFi calling. If that still doesn’t work, try it from a different WiFi connection. The issue could be your home internet.

Thank you sandblaster I will give that a shot!

If one is to use WiFi-C,  the recommendation is to place the phone in Airplane Mode to disable its cellular radio so the phone can only connect to your WiFi signal. The reason is that the phone will connect to the stronger of the two signals if both are active (MicroCell's 3G or WiFi), which can cause connection problems as you move around because the cellular and WiFi signal will vary.

If your MicroCell was deactivated by AT&T that should not have happened, yet, if it was still active and you were using it. AT&T is sending out notices warning folks that their MicroCell accounts will be deactivated by a specific date due to inactivity if they don't start using them again.

I've had two notices in the last year and each time I just took it out of its box (we use WiFi-C exclusively now with our iPhones), plugged it in and 8 minutes later it was active and usable. In fact, I just did that the other day as a test for someone and it's working just fine.

If you haven't made any changes to your account (change phone number, moved to a new location, etc) then the MicroCell should work just fine for now. That being said, the myAT&T MicroCell Settings page is broken and AT&T will not be fixing it as they have moved those resources to other projects. I can access my settings page but if i attempt to make a change, it won't allow it.

Unplug the MicroCell so that it is completely powered off and setup WiFi-C again. The radiant barrier in you home should have no effect on either one. We had a house with a new metal roof and the MicroCell and WiFi-C worked just fine. However, you do need a decent and robust WiFi connection for WiFi-C to work adequately. Most WiFi setups are fine.

Also putting the phone in airplane mode and turning your Wi-Fi back on will proof weather Wi-Fi calling is active on your phone at all or not.  

If your phone kicks back the message to turn off airplane mode in order to make a call, you know something is seriously amiss.

The iPhone should indicate AT&T WiFi when you pull down the control panel if WiFi-C is active, or it will indicate AT&T M-Cell if using the MicroCell connection. It's also not uncommon for the phone to just indicate AT&T and signal strength if that is the strongest signal at that point in time.