[Google Pixel 3 XL ROMs, Kernels, Recoveries, & Oth] Brainium:
I can confirm that wifi clling DOES NOT work, and I am on Xfinity Mobile. I am running my own build as well, (basically the same). Here are the logcat entries (different from the ones [MENTION=9798973]queuecumbr[/MENTION] posted):

02-25 16:26:18.912 22133 22133 D SettingsActivity: Switching to fragment com.android.settings.wifi.calling.WifiCallingDisclaimerFragment
02-25 16:26:18.912 22133 22133 D SubSettings: Launching fragment com.android.settings.wifi.calling.WifiCallingDisclaimerFragment
02-25 16:26:18.915 22133 22133 D LocationPolicyDisclaimer: [1] shouldShow: false due to carrier config is false.
02-25 16:26:18.917 22133 22133 D EmergencyCallLimitationDisclaimer: [1] shouldShow: false due to carrier config is default(-1).
02-25 16:26:18.926 22133 22133 D SettingsActivity: Executed frag manager pendingTransactions
02-25 16:26:18.934 22133 22133 D WifiCallingForSub: WFC activity request = 2 result = -1
02-25 16:26:18.938 1343 4138 I ActivityTaskManager: START u0 {cmp=com.google.android.wfcactivation/.VzwEmergencyAddressActivity (has extras)} from uid 1000
02-25 16:26:18.948 895 895 D android.hardware.power@1.3-service.pixel-libperfmgr: LAUNCH: 1
02-25 16:26:18.961 22133 23423 W TileUtils: Found com.android.settings.Settings$DataUsageSummaryActivity for intent Intent { act=com.android.settings.action.SETTINGS pkg=com.android.settings } missing metadata com.android.settings.category
02-25 16:26:18.975 22133 23408 D SettingsActivity: No enabled state changed, skipping updateCategory call
02-25 16:26:19.041 22133 22133 D WifiCallingSettings: Adapter getCount 1
02-25 16:26:19.042 22133 22133 I chatty : uid=1000(system) com.android.settings identical 1 line
02-25 16:26:19.043 22133 22133 D WifiCallingSettings: Adapter getCount 1
02-25 16:26:19.050 867 867 D Zygote : Forked child process 23426
02-25 16:26:19.052 1343 1382 I ActivityManager: Start proc 23426:com.google.android.wfcactivation/u0a140 for activity {com.google.android.wfcactivation/com.google.android.wfcactivation.VzwEmergencyAddressActivity}
02-25 16:26:19.057 23426 23426 E d.wfcactivatio: Not starting debugger since process cannot load the jdwp agent.
02-25 16:26:19.096 23426 23426 D ApplicationLoaders: Returning zygote-cached class loader: /system/framework/android.hidl.base-V1.0-java.jar
02-25 16:26:19.097 23426 23426 D ApplicationLoaders: Returning zygote-cached class loader: /system/framework/android.hidl.manager-V1.0-java.jar
02-25 16:26:19.097 23426 23426 D ApplicationLoaders: Returning zygote-cached class loader: /system/framework/android.hidl.base-V1.0-java.jar
02-25 16:26:19.099 23426 23426 I d.wfcactivatio: The ClassLoaderContext is a special shared library.
02-25 16:26:19.104 23426 23426 I d.wfcactivatio: The ClassLoaderContext is a special shared library.
02-25 16:26:19.126 23426 23426 W d.wfcactivatio: Couldn't clamp region space as there are regions in use beyond growth limit.
02-25 16:26:19.139 23426 23426 D WfcActivationActivity: Start Activity with subId : 1
02-25 16:26:19.141 23426 23426 D RadioConfigLib: askQcRilHook
02-25 16:26:19.143 611 611 E SELinux : avc: denied { find } for service=qchook pid=23426 uid=10140 scontext=u:r:priv_app:s0:c512,c768 tcontext=u:object_r:qchook_service:s0 tclass=service_manager permissive=0
02-25 16:26:19.144 23426 23426 E RadioConfigLib: Failed to create QcRilHookExt java.lang.IllegalStateException: Failed to find IService by name [qchook]
02-25 16:26:19.148 23426 23426 D WfcActivationActivity: Loading dependencies...
02-25 16:26:19.153 23426 23426 D WfcActivationActivity: Start Activity intention : 0
02-25 16:26:19.164 23426 23426 D WfcActivationActivity: Start VoWiFi activation flow.
02-25 16:26:19.171 23426 23426 D WfcActivationActivity: Next state is 1
02-25 16:26:19.172 23426 23426 D WfcActivationActivity: Query SSO token...
02-25 16:26:19.173 23426 23452 E ActivityThread: Failed to find provider info for com.verizon.loginclient
02-25 16:26:19.173 23426 23452 E WfcActivationActivity: Cannot read SSO database.
02-25 16:26:19.181 23426 23426 D WfcActivationActivity: SSO token not available, updating...
02-25 16:26:19.192 23426 23426 D WfcActivationActivity: SSO token updating error: 12

Also, some interesting information, when I was running a build WITHOUT the commits to use CarrierSettings, WiFi calling DID enable but wouldn't work. Upon dirty flashing a build with those commits, wifi calling DID work, and was already enabled. HOWEVER, it would not go through the emergency address setup process, and would show the same error.

Another question, is anyone else not seeing automatic call screening in the Google dialer app? Not just the regular call screening, but the new one. This also worked before, as with wifi calling.