How does SIP telephony work, and why do businesses use it? We explain IP telephony, its benefits and security requirements, and how eXpress combines phone calls, chats and video conferences in one application.
What is SIP telephony?
SIP telephony is a voice communication technology in which calls take place over any IP network, including closed networks that are not connected to the internet. The acronym stands for "Session Initiation Protocol"—a protocol used to establish, modify, and terminate multimedia communication sessions.
Simply put, it is a set of rules that allow devices to "agree" on how to begin and end a conversation. SIP has become the cornerstone of VoIP (Voice over IP) technology; unlike legacy telephone networks, it enables the transmission of voice, video, and data over a network, providing the flexibility and scalability characteristic of modern communication systems.
To users, the experience resembles an ordinary phone call: dial a number and speak. Calls can be made using:
- a SIP phone, which looks like a conventional telephone connected to an IP network;
- a smartphone with a dedicated application;
- a computer with a headset and softphone software.
What problems does SIP solve for businesses?
According to TMT Consulting, 540,700 companies in Russia used SIP telephony based on virtual PBXs by the end of 2025. The technology is especially useful for large organizations with high call volumes. A virtual PBX can distribute incoming calls, configure queues and track workloads.
SIP brings remote employees and teams in different cities into a single phone network. Customers call a shared number, and the call reaches an available employee's computer or smartphone regardless of location.
The technology is also useful for call analytics. With a virtual PBX, managers can review statistics and recordings to assess the effectiveness of customer calls and sales teams.
When employees call customers from offices, homes or other locations, a SIP application lets the company retain corporate numbers and centralized call handling. Routing, recordings and CRM connections remain within the corporate telephone system.
Which companies benefit from SIP?
Call centers and sales departments. With multi-channel phone numbers and call recording, companies can efficiently handle thousands of calls per day.
Retail and online stores. Easy-to-configure voice menus and call forwarding help improve customer service.
Financial and insurance organizations benefit from technology that ensures the protection of client data and precise quality control of calls.
Logistics companies use SIP to gain flexible communication between branches, remote offices, and drivers.
How SIP telephony works and what it supports
Call recording, routing, CRM integration and information security mechanisms are not part of the SIP protocol itself. They are functions of the surrounding infrastructure that works with SIP/RTP streams.
CRM integration also operates outside SIP signaling. A telephone system, such as a cloud PBX, generates events for incoming and outgoing calls, answers and hang-ups, then sends them to a CRM through an API. SIP therefore serves as a source of call events.
SIP security
Securing SIP connections is essential. Risks include stolen SIP credentials, call interception or eavesdropping, call spoofing and diversion, unauthorized premium-rate calls and attacks on service availability. Vulnerabilities in PBXs, SIP clients and IP phones pose additional threats.
Recommended protections include TLS for SIP signaling and SRTP for encrypted voice traffic, strong unique passwords, and access restrictions using firewalls or session border controllers (SBCs). Organizations should also limit authentication attempts, keep software updated and monitor suspicious connections and calls.
SIP telephony in eXpress
SIP telephony within a unified communications platform integrates SIP calling into one corporate workspace. eXpress brings internal chats, video conferencing and external phone calls together in a single application. Development of this functionality began in 2021.
eXpress is available on iOS, Android, web and desktop and acts as a softphone connected to the customer's PBX. Integration requires installation and configuration of server components, as described in the administrator documentation for IP and SIP telephony.
Key SIP capabilities in eXpress include:
- adding participants to eXpress group calls and conferences using internal SIP numbers, including integration with Vinteo conferencing servers;
- dialing extensions, IP addresses or SIP URIs through an in-call keypad;
- choosing IP telephony or the mobile network for numbers without a specified prefix;
- video in one-to-one SIP calls, enabled by a server administrator;
- video calls over IP telephony;
- TURN/STUN support for calls across NAT and private corporate networks;
- a history of individual SIP calls alongside other calls;
- displaying the IP telephony number in the user profile with click-to-call;
- displaying SIP terminal room numbers and conference connection details, including when copying conference links;
- inviting a participant by phone number into an active SIP conference;
- minimizing the call window, viewing signal strength and muting the microphone;
- searching the corporate contact directory when enabled on the server;
- calling directly from a contact card or chat;
- displaying the caller's name and number;
- push notifications for incoming and missed SIP calls;
- SIP conference recording, which is under development.
SIP user documentation is available in the eXpress Knowledge Base.
Business benefits
SIP telephony in a unified communications platform brings separate communication channels into a single system. It can reduce the need for expensive employee telephone hardware and, in some cases, additional cabling. It also helps businesses organize remote teams and call centers quickly. Recording and reviewing calls can support service quality assessments.
By deploying SIP telephony within eXpress, a company effectively creates a virtual office. Employees can work faster, maintain oversight of workflows and stay in touch with customers from different locations.