There is definately some troubleshooting we can do to resolve the issue.
In order to use Wi-Fi Calling on this phone, a GBA SIM card is required and provisioned with Wi-Fi Calling. These errors can occur if the SIM card being used is not a GBA SIM card or if a GBA SIM is not provisioned for Wi-Fi Calling, most likely because the SIM card has not received the Download OTA.
Oh, I found the document explaining a "GBA sim card" (Purchasing a SIM card, below). I should make clear that I get ER05 only on restart when WiFi calling is enabled. If I power WiFi off and on again with a registered/saved SSID in range, I get the pretty blue Wifi-Calling icon. If i turn Wifi-Calling off and on again under the same proper conditions, I get the blue icon. If I change connection preferences, too (I think), it works.
I seem to recall a similar issue in December when the 1.43 update introduced Wi-Fi Calling on the Amaze.
I think the problem is one referred to in the following document. That is, on power-up, the SIM is not quite ready or has not be fully read yet, and WiFi-Calling is active before this, resulting in an error. That indicates a startup script (init.d) problem that has to be fixed by T-Mo or HTC.
I've confirmed as per the following document that I have a "GBA" SIM card, with TM9177 imprinted on the back.
I am on the monthly prepaid plan and had a Sensation 4G with WiFi calling enabled and working.
After switching to an Amaze 4G and using the same SIM card I got the WiFi Calling error "Invalid SIM card".
Went to the TMobile booth in the Quaker Bridge mall (NJ) and the associate was right on it - he took out the old SIM and programmed a new one. No charge.
All good now (although I did have to go to the TMobile site and set up a profile with a 911 address)