Call processing methods and apparatuses are provided in a Session Initiation Protocol (SIP) based network involving at least one Push-to-Talk (PTT) over Cellular PoC client and a reception side PoC server. The reception side PoC server receives an INVITE request including a Manual Answer Override (MAO) indication from a transmission side PoC server. The MAO indication is for establishing an auto-answer mode in a pre-established session. If a reception side PoC client has the pre-established session with the reception side PoC server, the reception side PoC server sends an OK response to the transmission side PoC server in response to the INVITE request. The reception side PoC server sends a communication connection request including the MAO indication to the reception side PoC client. The MAO indication is used to determine that a transmission side PoC client is an authorized user with respect to the reception side PoC client.