The GetDisplayName function returns the display name
associated with a supplied SIP address.
The SIP address whose associated display name portion will be
parsed and returned; for example, GetDisplayName("\"Display Name\"
<sip:firstname.lastname@example.org:6767>") returns the string
"Display Name". (Note that the double quotes around the display
name in the address must be escaped if a literal is passed
directly, rather than as the output of another function, such as
Returns the display name as a string. Returns null if requested
data is not found.