Help Galaxy S5 ER05-Invalid SIM message for WiFi Calling??

[OldIron01]

I have the unlocked SM-G900T with the Marshmallow OS, and I am using it with AT&T service..

All seems well after setting up the APN, except one oddity.

The WiFi Calling doesn't work. When attempting activate WiFi Calling, it indicates "Er05 - Invalid SIM".

I went to AT&T, and they changed the SIM, no help. The Samsung rep at BestBuy indicated he had no idead, but he suspected it was an issue with a T-Mobile phone being used on an AT&T network?

I searched the forums, both here and abroad and haven't found any solution yet.

Any ideas on how to fix this, or if it's even possible?

Maybe I should just install one of the Google Phone apps?

Thanks in advance...

P.s. I got the APN settings from AT&T, and they matched here under :

http://apn-settings.com/us/att-apn-settings/

Name: ATT HSPA+
APN: phone
Proxy: <Leave in Blank>
Port: <Leave in Blank>
Username: <Leave in Blank>
Password: <Leave in Blank>
Server: <Leave in Blank>
MMSC: http://mmsc.mobile.att.net
MMS proxy: proxy.mobile.att.net
MMS port: 80
MCC: 310
MNC: 410
Authentication type: <Leave in Blank>
APN type: default,supl,mms,hipri, fodo
APN Protocol: Leave it to the Default one
Bearer: leave it to the Default one

 

[mikedt]

The Best Buy, Samsung rep is probably correct actually. It could be because this is a T-Mobile version phone, that its WiFi calling service is still trying to connect to T-Mobile's servers. And because it hasn't got T-Mobile service and SIM, they're refusing access.

WiFi calling is only provided on phones supplied by the carriers themselves.

To fix it, I think you might have to see about changing the ROM to an AT&T version, that has the AT&T WiFi calling service, that's just a guess mind.

Non-carrier version phones just don't have carrier provided WiFi calling.