2.2.5.1 PidTagSenderTelephoneNumber Property
Type: PtypString ([MS-OXCDATA] section 2.11.1.2)
The PidTagSenderTelephoneNumber property ([MS-OXPROPS] section 2.1008) contains the telephone number of the caller associated with a voice message.
The relationship between this property and the X-CallingTelephoneNumber MIME header is specified in [MS-OXCMAIL] section 2.1.3.2.3.