Carrier-grade voice communications continue to move away from traditional analog systems in favor of SIP phones. The SIP phone market is forecasted to reach $3.3 billion by the end of 2025,1 likely driven by the need to deliver scalable, flexible voice solutions. Cellular SIP-based solutions contribute to this by bringing the SIP phone into every mobile device.
But what is a SIP phone, and why has it become the standard for so many telecom and large enterprise networks? In this guide, we’ll break down how SIP phone systems work, the different types available, and what technical teams should consider when deploying them at scale.
A SIP phone is a voice-over-IP (VoIP) endpoint that uses the Session Initiation Protocol (SIP) to manage voice or video calls over an IP network. Unlike legacy analog phones that connect through the PSTN, SIP phones rely on IP connectivity to reach other devices and services.
There are two main types of SIP phones: hardware-based, which are physical desk phones with SIP firmware, and software-based (softphones), which run on a computer or mobile device. The software inside a modern smartphone, iPhone, or Android, is a type of SIP phone. Both types register with a SIP server and use standard SIP messages to handle call setup, negotiation, and teardown.
ECG supports large-scale SIP phone installations by designing the configuration files and device management systems to enable activation of new SIP phones for a service provider. We also support eSIM integration, which allows cellular/mobile networks to connect to VoIP platforms. Plus, ECG can customize and brand SIP software to match the needs of enterprises and service providers.
SIP phone systems work by connecting phones to a SIP service provider or PBX, which may be run on-premises (a data center you run) or hosted in the cloud (a data center run by someone else). Each phone registers with the server and is assigned a unique extension or direct-dial number.
Whenever a user places a call:
Depending on the network architecture, SIP traffic can be routed over the public internet, MPLS, VPN tunnels, or private fiber.
Cybersecurity is a major concern for SIP phones and must be addressed. Device management is often the first target for attackers, since gaining a SIP phone configuration would allow an attacker to perform a "SIM swap" equivalent and take over a user’s service. This could lead to a loss of privacy or fraudulent use of the services.
Apart from device management, SIP phones use SIP REGISTER, which is subject to other types of attacks that can potentially exploit weak SIP authentication credentials. And finally, once calls are happening, attacks like RTP bleed and RTP injection must be managed using SBCs and server implementation and configuration.
Not all VoIP phones use SIP; some use proprietary signaling protocols that lock users into specific platforms. For example, Microsoft Teams phones don’t use SIP, but instead a proprietary protocol. SIP phone service is based on an open standard, which allows for interoperability between devices, servers, and platforms from different vendors.
This makes SIP phones the only choice for organizations that use multi-vendor environments or manage distributed systems. Voice service providers, ISPs, and enterprise IT teams can deploy SIP phones across various hardware, UCaaS platforms, and SBCs with consistent behavior. It also makes SIP phones the standard for service providers, large and small, who want to offer a variety of phones to their clients.
Different environments call for different SIP telephone types. Here are the most common options:
These are physical desk phones that function like traditional telephones but include an Ethernet port and embedded SIP firmware. They usually support PoE (Power over Ethernet), multiple lines and extensions, and wideband audio codecs like G.722.
Hard SIP phones are commonly deployed in NOCs, call centers, and office environments where users need a dedicated, always-on device. You can typically find them in reception areas, kitchens, break rooms, and manufacturing facilities where wireless communication may not be reliable.
Softphones are applications installed on a PC, Mac, tablet, or mobile device and rely on the host device’s microphone and speakers. The most common softphone is actually running inside every smartphone! Modern cellular networks that use 4G LTE or 5G operate SIP networks to provide voice service.
Softphones are primarily used in remote work setups and mobile support teams. They also integrate with UCaaS dashboards, CRM tools, or collaboration apps, making them ideal for modern, integrated phone systems.
Some hard SIP phone systems support video calling. These devices include integrated cameras and video codecs (e.g., H.264) and are typically used in executive offices, telemedicine, or high-touch customer interactions.
A wireless SIP phone uses Wi-Fi or DECT instead of Ethernet to connect. This makes them helpful for use on warehouse floors, in hospitals, or on enterprise campuses where users need constant mobility and communication.
Let’s explore common SIP phone examples and where businesses deploy them:
Each device supports SIP signaling and RTP media streams, but the form factor and features vary to fit different deployment needs. Keep in mind that many modern phones are built on Android, which requires special care for security.
Whether deployed by a regional voice service provider or a state government IT department, SIP phone systems offer several advantages to businesses. These include:
SIP’s open protocol allows seamless interoperation between voice platforms like Cisco CUCM, BroadWorks, Metaswitch, NetSapiens, PortaOne, Microsoft Teams, Metaswitch Perimeta, and Oracle SBCs. As a result, organizations can use SIP to deploy phones across multiple systems as needed.
SIP phones eliminate the need for analog gateways, PRI lines, or legacy PBX hardware. Plus, a single SIP trunk can support multiple concurrent calls, and centralized provisioning simplifies large-scale deployments – all of which adds up to lower deployment costs.
SIP phones support modern features like:
These features make SIP phones ideal for carrier and enterprise-grade voice deployments.
SIP phone service can route around outages using SRV failover, DNS load balancing, or geo-redundant SBCs. They can also auto-re-register to a backup server if the primary fails, reducing downtime.
ECG frequently designs high-reliability networks and integrates fault tolerance setups using DNS, SBCs, IP address sharing, BGP routing, and SD-WAN, ensuring that end users experience the best possible experience with their SIP phones.
SIP phones give organizations more control over how and where voice services are delivered. Teams can mix and match hard phones, softphones, and wireless SIP devices based on user roles, without requiring changes to the infrastructure.
Deploying SIP phone systems at scale – especially across telco or ISP networks – requires detailed planning. Important factors to consider include:
Since SIP phones are internet-connected endpoints, they can expose your entire network to attacks or service disruption without proper safeguards. Taking the time to plan each of these areas is essential for protecting your infrastructure and delivering high-quality voice services.
SIP phones are at the foundation of modern IP voice networks. Their flexibility, scalability, and interoperability make them essential for any business delivering telecom services, whether you're supporting call centers, municipal networks, or federal IT systems.
At ECG, we help voice service providers, ISPs, and government agencies deploy, troubleshoot, and optimize SIP phone systems at scale. If you need expert engineering guidance – from secure provisioning to end-to-end call path analysis – we’re here to help.
Reach out to the ECG team today to talk about how we can support your SIP deployments.
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