For details about how to configure the SIP value-added services such as hotline services and call transfer, see the OLT Voice Feature Guide at the following link: http://support.huawei.com/hedex/hdx.do?docid=DOC1000357950&id=cfg_cli_4380&text=Configuring%25252520SIP%25252520Value-added%25252520Services&lang=en