Cisco SPA301 Administration Manual page 331

Cisco SPA IP Phone Field Reference
Ext Tab
Cisco Small Business SPA300 Series, SPA500 Series, and WIP310 IP Phone Administration Guide
Parameter
User Equal Phone
Description
When a tel URL is converted to a SIP URL and the
telephone number is represented by the user portion of
the URI, the SIP URL includes the optional :user=phone
parameter (RFC3261). For example:
To: sip:+12325551234@example.com;user=phone
To enable this optional parameter, choose yes. The default
value is no.
A
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