Each phone's own settings and modem file, against what that phone had before.
{ "Media": { "IncludeSDPModeChangeCapability": true }, "Signaling": { "EarlyMediaNeedsHeader": false, "AdditionalContactParams": { "REGISTER,INVITE,INVITE:*": "+g.3gpp.mid-call;+g.3gpp.srvcc-alerting;+g.3gpp.ps2cs-srvcc-orig-pre-alerting" }, "AlwaysSendSessionProgress": true, "InviteErrorResponsesToTriggerCSFB": "403,408,5XX", "UseIPSec": true, "SupportPEarlyMediaHeader": false }, "XCAP": { "supported": false }, "Voice": { "EnableVolteByDefault": true }, "SMS": { "SupportedDomains": { "GSM": false, "LTE": false, "UMTS": false } } }