The Definitive Guide to VoIP Security and Encryption in 2025

With the traditional phone network – the Public Switched Telephone Network (PSTN) – set to be switched off by 31 January 2027, BT is urging UK businesses to adopt Voice over Internet Protocol (VoIP) solutions by the end of 2025 to avoid service disruptions. VoIP converts your voice into digital data packets that travel over the internet, rather than traditional phone lines.

Unfortunately, this shift happens as online security threats continue to grow. Understanding how to protect your business phone conversations as they travel across the internet has never been more important. In this guide, we’ll tell you everything you need to know about securing VoIP in 2025.

Key Takeaways

• Modern VoIP systems face a wide range of cyber threats from basic eavesdropping to sophisticated ransomware attacks.
• UK businesses must consider data privacy regulations, including GDPR, while ensuring their VoIP provider meets compliance standards.
• Encryption technologies like TLS, SRTP, and VPNs are essential for protecting sensitive voice data, especially with remote workers.
• Using secure VoIP providers, strong passwords, multi-factor authentication (MFA), and regular updates forms the foundation of VoIP security.

What Is VoIP Security? A 2025 Definition

While traditional phones use copper wires to transmit voice signals (meaning someone would need physical access to tap your line), VoIP communications travel across the same networks as your emails and web browsing, sharing similar security vulnerabilities.

Therefore, VoIP security is everything that protects your:

1. VoIP devices: This includes desk phones specifically designed for internet calling (IP phones) and software programs that turn computers or smartphones into phones (softphones).
2. Network infrastructure: The routers, switches, and firewalls that handle your internet traffic, including VoIP calls.
3. Endpoints: The computers and mobile devices people use to make or receive VoIP calls.

How VoIP Keeps Your Data Safe

VoIP includes several security technologies designed to protect your conversations, provided they’re properly configured. Here are some of the key protective measures:

Transport Layer Security (TLS)

Transport Layer Security (TLS) encrypts the ‘signalling’ – all the behind-the-scenes information exchanged before your call even starts. This includes details like who’s calling, the number being dialled, and how to route the call.

Think of TLS as the secure envelope for your call setup information. Without it, attackers could see who you’re calling and potentially gather sensitive business intelligence.

Secure Real-Time Transport Protocol (SRTP)

If TLS protects the call setup, Secure Real-Time Transport Protocol (SRTP) protects the actual conversation. It encrypts the voice data packets (your digitised speech) as they travel across the internet.

SRTP works by:

• Using strong encryption algorithms (typically AES – Advanced Encryption Standard) to scramble voice data so that only authorised recipients can unscramble it
• Verifying that voice packets haven’t been tampered with during transit
• Preventing ‘replay attacks’ where recorded packets could be sent again later

Without SRTP, your calls could potentially be intercepted and listened to by attackers with access to the network.

Virtual Private Networks (VPNs)

A Virtual Private Network (VPN) creates a secure, encrypted tunnel for all your internet traffic, including VoIP. This is especially important for remote workers using home Wi-Fi or public networks.

When you use a VPN, all data leaving your device is encrypted before it reaches the potentially insecure public internet. Even if someone could intercept the data, they wouldn’t be able to read it without the encryption key.

For businesses with staff working remotely, VPNs provide an additional layer of security for VoIP calls made outside the protected office environment.

Emerging technology: ZRTP

ZRTP (Zimmermann Real-time Transport Protocol) offers enhanced security by negotiating encryption keys directly between the devices on each end of the call. This ‘end-to-end encryption’ means that even your VoIP service provider can’t access the content of your calls.

While not yet universal, ZRTP is worth considering for highly confidential communications where maximum privacy is required.

VoIP Security Compliance and Regulations in 2025

UK businesses using VoIP must comply with various data protection regulations:

• General Data Protection Regulation (GDPR): This applies to all personal data processed during VoIP calls, including recordings and caller information. You need legal grounds to collect this data and must implement appropriate security measures to protect it.
• Payment Card Industry Data Security Standard (PCI DSS): If your business takes credit card payments over the phone, your VoIP system must comply with PCI DSS requirements. This may include call encryption and restrictions on recording card details.
• Healthcare confidentiality rules: Healthcare organisations must ensure patient information shared during VoIP calls remains confidential and secure.
• ISO 27001: While not legally required, this international security standard demonstrates your commitment to information security best practices and may be expected by larger clients.

Additionally, the upcoming Cyber Security and Resilience Bill, expected in 2025, will introduce mandatory reporting requirements for major cyber incidents, including ransomware attacks.

Top VoIP Security Threats in 2025

The VoIP systems of UK businesses face several security threats:

Eavesdropping and interception

Without proper encryption, attackers using tools called packet sniffers can capture and access the content of your calls as they travel across networks. This is similar to someone intercepting and reading your post before it reaches its destination.

In practical terms, this means a competitor or criminal could potentially listen to your business negotiations, client conversations, or internal discussions if your calls aren’t properly secured.

Phishing and vishing attacks

You’re likely familiar with email phishing (fake emails trying to trick you into revealing information), but ‘vishing’ (voice phishing) is its telephone equivalent. Typically, victims receive an email from what appears to be a trusted source asking them to call a number. When they call, imposters try to extract sensitive information, such as passwords or financial details.

To make these calls seem legitimate, attackers often use caller ID spoofing – technology that makes their call appear to come from a trusted number, like your bank or IT department.

Toll fraud

Toll fraud, also known as international revenue share fraud (IRSF), is a serious problem where criminals break into a company’s phone system to make expensive long-distance calls without permission.

The fraudsters receive a percentage of the call revenue generated from these premium-rate calls. In some cases, they’re part of organised crime rings that specifically target enterprise VoIP systems, potentially causing tens of thousands of pounds in losses before the fraud is detected.

DDoS attacks on VoIP networks

A Denial of Service (DoS) attack aims to make your phone system unavailable by flooding it with so much junk traffic that legitimate calls can’t get through. Think of it as thousands of people calling your phone simultaneously so that important calls can’t connect.

In a Distributed Denial of Service (DDoS) attack, hackers use multiple computers from different locations to launch this flood of traffic, making it harder to block. For businesses that rely on phone communications, such attacks can effectively shut down operations.

Outdated systems and firmware

Using outdated software or hardware creates a serious risk. Manufacturers regularly release updates (called patches or firmware updates) that fix security vulnerabilities they’ve discovered. If you don’t apply these updates, you leave known security gaps that attackers can exploit.

For example, researchers discovered a decade-old vulnerability in some Avaya VoIP phones that could allow attackers unauthorised access to eavesdrop on conversations. Regular updates would have protected against this risk.

Best Practices for Securing VoIP in 2025

Protecting your VoIP system requires a combination of the right technology choices and smart operational practices:

1. Choose a secure VoIP provider: Look beyond price to security credentials. Check if it operates secure data centres, offers encryption (TLS/SRTP) by default, meets compliance standards like ISO 27001, and provides strong uptime guarantees. Our guide to the best UK VoIP providers can help you compare options.

Pro tip: Ask providers specifically how they protect against DDoS attacks and if they use multiple data centres for redundancy in case one location experiences problems.

2. Encrypt VoIP traffic: Don’t assume your calls are automatically encrypted. Actively enable TLS (for call setup) and SRTP (for voice data) in your system settings. For staff working outside the office, implement a reliable VoIP VPN to secure their connection.

3. Update devices and firmware regularly: Just as you update your computer and smartphone, keep all VoIP equipment current. This includes firmware on desk phones, softphone applications, and operating systems on all devices that connect to your VoIP service.

4. Use strong authentication and MFA: Implement complex, unique, strong passwords for all user accounts and admin access. Strong passwords combine upper and lowercase letters, numbers, and symbols. MFA adds a second verification step (usually a code sent to a mobile device) to ensure that even if passwords are compromised, accounts remain secure.

5. Segment network traffic: Keep voice traffic separate from general data using Virtual Local Area Networks (VLANs). This is like giving your voice traffic its own lane on the information highway.

6. Implement firewall rules and intrusion detection: Configure your firewall specifically for VoIP by allowing only necessary traffic and blocking potential threats. Consider using intrusion detection systems that automatically monitor for suspicious activity like unusual login attempts or unexpected calling patterns.

7. Train employees on VoIP risks: Your staff are both your first line of defence and a potential vulnerability. Educate them about vishing calls, phishing emails targeting VoIP logins, password security, and proper procedures for reporting suspicious activity.

8. Monitor VoIP logs and call patterns: Regularly review your system’s activity logs and call records. Look for unusual patterns like calls at odd hours, unexpected international numbers, spikes in call volume, or multiple failed login attempts – all potential indicators of security issues.

Future Trends in VoIP Security

VoIP security continues to evolve alongside both threats and protective technologies:

• AI in fraud detection: Artificial intelligence is increasingly analysing call patterns in real time to identify suspicious activities that might indicate fraud or attacks. AI can spot anomalies much faster than human monitoring alone.
• Post-quantum cryptography: Standard encryption methods could theoretically be broken by quantum computers in the future. The National Cyber Security Centre has outlined a plan for UK organisations to transition to quantum-resistant encryption methods by 2035, ensuring long-term security.
• Zero Trust architecture: The traditional security model assumed devices inside your network could be trusted. The Zero Trust model eliminates this assumption, requiring verification from all users and devices regardless of location.

VoIP Security in Remote and Hybrid Workforces

With hybrid working becoming standard practice in the UK, securing VoIP outside the office perimeter presents unique challenges. Home networks typically lack enterprise-grade security, and using VoIP for mobile devices introduces additional considerations.

To secure remote VoIP communications:

Require VPN use: Make it standard practice for remote employees to connect via a secure VPN before using VoIP services. This encrypts all their internet traffic, including voice calls, protecting them even on potentially insecure home or public networks.

Secure softphones: Softphones are applications that turn regular computers or smartphones into VoIP phones. Ensure these apps require strong passwords and keep them updated with the latest security patches.

Establish clear BYOD (Bring Your Own Device) policies: If allowing personal devices for work calls, create clear security requirements covering device locking, encryption, approved applications, and procedures for lost or stolen devices.

Ultimately, ensure your remote VoIP phone systems follow the same security standards as your office-based equipment.

How To Choose a Secure VoIP Provider

When selecting a VoIP provider, ask these essential security questions:

• Do you offer SRTP and TLS encryption by default, or does it require manual setup?
• What encryption strength do you use?
• Do you operate multiple, geographically separate data centres?
• What happens if there’s a security breach or service outage? How quickly will you notify us, and what support will be available?
• How do you handle security patches and firmware updates? Are they automatic or manual?
• Do you support MFA for user and administrator access?
• What security certifications do you hold? How do you help customers meet regulatory requirements?

Building a Secure VoIP Strategy With the Right Provider

Securing your business voice communications requires a strategic approach combining:

• Appropriate encryption technologies
• Security best practices for networks and devices
• Thorough employee training

Most importantly, you need a partnership with a security-focused VoIP provider. Our comparison of the best business VoIP providers in the UK can help you evaluate potential partners that prioritise security alongside features and pricing.