This document describes a private Session Initiation Protocol (SIP) header (P-header) used by the Open Mobile Alliance (OMA) for Push to talk over Cellular (PoC) along with its applicability, which is limited to the OMA PoC application. The P-Answer-State header is used for indicating the answering mode of the handset, which is particular to the PoC application. This memo provides information for the Internet community.