This document defines an eCall "Optional Additional Data" concept for the "Minimum Set of Data" (MSD) to be transferred from a vehicle to a 'Public Safety Answering Point' (PSAP) in the event of a crash or emergency via an 'eCall' communication transaction. This document defines: a) Protocol requirements to ensure phone user consent to the provision of the linked 'phone number to the PSAP in the event of an eCall triggering incident; b) Definition of the OAD concept "Linked mobile Telephone Number" (LTN); c) Privacy provisions; d) Advice to PSAPs on the use of the eCall OAD LTN; e) Example of an in-vehicle sequence generating the LTN OAD and forwarding it as part of the MSD. For clarity, the communications media protocols and methods for the transmission of the eCall message are not specified in this document.