The header format used by the system is set by the setting. This has the following options:
SIP - Use sip: format SIP URIs.
Tel - When selected, the system uses the Tel URI format, for example tel:+1-816-555-1212, in To headers.
SIPS - When selected, the system replace the sip: part of the SIP URIs it sends with sips:. That indicates that TLS must be used for all stages of the call. To use this, the line's Layer 4 Protocol needs to be set to TLS.
