VoIP phone

As mainstream operating systems became better at voice applications with appropriate quality of service (QoS) guarantees, and 5G handoff (IEEE 802.21 etc.)

iPhone, Android and the QNX OS used in 2012-and-later BlackBerry phones are widely capable of VoIP performance.

The smartphone became the dominant VoIP phone because it works both indoors and outdoors, and shifts base stations/protocols easily.

It achieves this by accepting higher access costs and call clarity, and other factors personal to the user.

A Session Traversal Utilities for NAT (STUN) client is used on some SIP-based VoIP phones as firewalls on network interface sometimes block SIP/RTP packets.

STUN or any other NAT traversal mechanism is not required when the two SIP phones connecting are routable from each other and no firewall exists in between.

While a license is required to run a cellular base station in most countries, these can be useful on ships, or in remote areas where a low-powered gateway transmitting on unused frequencies is likely to go unnoticed.