No idea what the gb??? SIM card is, but as to the wifi calling.
Most TM phones can do wifi calling, my old TM phone had a icon that you had to use to wifi call through. Going through the regular diaper was normal call, if you used the other it was wifi call, it could wifi call over the phones 4g service (which was crap) or through your homes wifi if you had wifi on and cell data turned off.
Problem with TM wifi calling is that it still counts against your min. If your monthly plan is 1000 min and you use 500 on wifi, it was 500 off your total 1000 for the month.
Now if you have a unlimited plan this does to apply. But if you don't you need to be aware.
GBA is Generic Bootstrap Architecture. I didn't look to far in to what it meant but it kinda looked like it was a locked sim. Like the sim was locked to the phones hardware some how.
In mobile phones, Generic Bootstrapping Architecture (GBA) is one technology enabling the authentication of a user. This authentication is possible if the user owns a valid identity on an HLR Home Location Register or a Home Subscriber Server
GBA is standardized at the 3GPP (http://www.3gpp.org/ftp/Specs/html-info/33220.htm) . The user authentication is instantiated by a shared secret, one in the smartcard inside the mobile phone and the other is on the HLR/HSS.
GBA authenticates by making a network component challenge the simcard card and verify that the answer is similar by the one predicted by the HLR/HSS.
Instead of asking the service provider to trust the BSF and relying on it for every authentication request, the BSF establishes a shared secret between the simcard card and the service provider. This shared secret is limited in time and for a specific domain.
I get you some info and learn how to copy and paste on my IPad.