The M8 phone supports uploading the OpenVPN configuration file in phone web.
2.9 Quality of Service (QoS)
VoIP is extremely bandwidth- and delay-sensitive. QoS is a major issue in VoIP implementations regarding
how to guarantee that packet traffic is not delayed or dropped due to interference from other lower priority
traffic. VoIP can guarantee high-quality QoS only if the voice and the SIP packets are given priority over
other kinds of network traffic. IP phones support the 802.1P/DiffServ model of QoS.
Voice QoS