Value,Description,Reference
wired,A number of a wire-line (land-line) phone.,[RFC7970]
mobile,A number of a mobile phone.,[RFC7970]
fax,A number to a fax machine.,[RFC7970]
hotline,"A number to a regularly monitored operational
        hotline.",[RFC7970]
ext-value,"A value used to indicate that this attribute is
        extended and the actual value is provided using the
        corresponding ext-* attribute.  See Section 5.1.1 of [RFC7970].",[RFC7970]