VoIP (Voice over Internet Protocol) enables you to make phone calls over the internet instead of traditional cellular networks. Many modern apps and phone services now offer encrypted VoIP, where communications are scrambled using cryptographic techniques.
While encryption is an essential privacy tool, it doesn’t protect you from all digital threats. Even encrypted calls may leave behind a trail of metadata, such as who you called, when, and for how long, which can be accessible by various parties, including hackers and scammers.
Below, we’ll explain how encrypted VoIP works and why, despite its strengths, it still leaves you exposed in unexpected ways.
What Is Encryption in VoIP?
Encryption in VoIP refers to scrambling your voice data and call details so they're unreadable if intercepted. In practice, this happens by:
- Transit encryption
- End-to-end encryption (E2EE)
Transit encryption secures data as it travels between your device and the VoIP provider's servers, typically using protocols like Secure Real-time Transport Protocol (SRTP) for voice or text packets and Session Initiation Protocol (SIP) over Transport Layer Security (TLS) for call setup information like caller IDs. These protocols create an encrypted tunnel so that outsiders see only scrambled data, not the actual conversation or call metadata visible on the network.
End-to-end encrypted VoIP services take this further: only you and the person you're calling can decrypt the conversation using private keys stored locally on your device. The provider itself can't read the contents, even if it wanted to. E2EE is stronger but less common in traditional VoIP, although it's often used in privacy-focused apps like Signal or Session.
How Encryption Protects Against Common VoIP Security Risks
Encryption directly addresses several vulnerabilities that unencrypted VoIP systems face. Some of the most common VoIP threats are explained below:
- Call interception and eavesdropping: Attackers can use packet-sniffing tools such as Wireshark to intercept unencrypted VoIP traffic and reconstruct entire conversations in real time. Encryption makes these packets unreadable to attackers, meaning they only capture gibberish, not your actual voice.
- Man-in-the-middle (MitM) attacks: In MitM attacks, hackers position themselves between the two parties and exploit SIP vulnerabilities to hijack calls via a redirection server. TLS encryption protects SIP signaling, preventing attackers from reading or modifying call initiation or registration requests.
- Unauthorized call recording and provider logging: E2EE prevents outsiders, including the provider itself, from observing or recording your call or message content. Note that basic transit encryption doesn’t protect against provider logging. Encryption also doesn’t stop the provider from logging call metadata—who you called, when, and for how long—and retaining records for extended periods.
That said, the level of protection you get depends heavily on the provider. Many VoIP apps advertise “secure” or “encrypted” communication but still retain extensive metadata indefinitely or tie activity to a long-lived phone number and account identity. Some may even share this sensitive information with business partners or third parties, depending on their data policies.
This becomes especially important when people use VoIP numbers as burner or secondary numbers. On paper, disposable VoIP numbers seem like the perfect privacy solution to keep your primary line private. In practice, your identity and metadata remain in the provider's hands.
Cape is a privacy-first mobile carrier built to address these fundamental provider-level threats. The carrier minimizes the amount of data collected (we don’t even ask for your name) and retains it for only as long as required.
Instead of relying on vulnerable VoIP infrastructure for virtual numbers, Cape offers real eSIM-based secondary numbers designed for true compartmentalization. You get up to two secondary numbers included with your plan, which you can use for:
- Online shopping
- Signups
- Sensitive 2FA flows
- Communicating with strangers
Encryption Models of Popular VoIP Calling Apps
Encryption models vary significantly across VoIP and messaging services. Some platforms use true E2EE for messages but not for actual metadata. Others rely primarily on transit encryption, which protects your calls from interception while moving across the network but still leaves the provider with access to decrypted content.
The table below compares the encryption levels of some of the common VoIP platforms:
App/Service | Encryption Type | Notes |
E2EE by default | One of the strongest mainstream options for private calls and messaging. Signal minimizes metadata collection, but it still relies on phone numbers as account identifiers. | |
E2EE by default | Uses the Signal Protocol for message and call encryption. However, metadata and account activity may be tied to the broader Meta ecosystem. | |
Transit encryption by default; E2EE optional for Secret Chats | Standard Telegram calls are encrypted, but Secret Chats must be enabled manually for full E2EE messaging. Metadata is still provider-accessible. | |
Google Voice | Transit encryption | Encrypts data in transit, but call metadata and activity remain tied to your Google account and infrastructure. |
Burner | Not disclosed publicly | Primarily designed for disposable numbers and compartmentalization rather than strong cryptographic privacy guarantees. |
Note that even strong E2EE on apps like WhatsApp or Signal doesn’t completely eliminate metadata exposure or identity risks tied to phone numbers themselves. Additionally, these apps have their own limitations: they require both parties to use the same app, and VoIP apps generally don’t work with account signup or verification flows.
Where Encrypted VoIP Still Falls Short
Even an encrypted VoIP service leaves several gaps that may expose you to various security and privacy threats. The most critical vulnerabilities include:
- Provider security infrastructure: Most VoIP systems require trusting the service provider. The provider manages your account and encryption keys, so if their infrastructure is compromised or they retain extensive logs, encryption can’t protect you. In effect, you are completely dependent on the carrier’s security practices and privacy policies.
- Endpoint security: Encryption protects data in transit, but not on devices. If your phone or virtual number app is infected with malware, attackers can capture your voice or credentials before they’re encrypted. Similarly, if the recipient’s device is hacked, even encrypted calls are exposed at that end.
- Configuration gaps: Encryption only works if it’s properly enabled end-to-end. In practice, misconfigurations or legacy fallbacks can introduce weak links. For example, many providers offer encryption as an optional service, rather than enforcing it by default. Some of them fail to enable TLS or SRTP everywhere, meaning the system may fall back to unencrypted RTP/SIP or calls may revert to plaintext without warning, leaving them exposed despite encryption being available.
On the other hand, Cape’s minimal-data approach reduces the amount of subscriber information that can be exposed, retained, or breached in the first place. Features like IMSI rotation are also designed to make long-term tracking significantly harder by regularly changing the subscriber identifiers tied to network activity.
VoIP Security Best Practices
Encryption solves one part of the problem, but VoIP services can still expose users through weak account security, insecure networks, social engineering attacks, and other threats. Here are some practical steps that help reduce those risks:
Strategy | Explanation |
Verify encryption is enabled | Don't assume your VoIP service has encryption turned on. Check your app settings and confirm encryption status before making sensitive calls. |
Use strong authentication | Enable multi-factor authentication (MFA) on your VoIP account. This prevents attackers from hijacking your account even if they obtain your password. |
Avoid public WiFi for sensitive calls | It’s much easier for hackers to intercept traffic or devices on public or shared networks. Instead, use cellular data or a trusted home network for important calls. |
Watch out for vishing attempts | Scammers spoof caller IDs and use persuasive social engineering tactics to trick you into revealing sensitive information, completely bypassing encryption or other protections. Never share sensitive information based solely on an incoming call; verify the caller's identity independently. |
A More Secure Alternative: Secondary Phone Numbers
Using a secondary phone number can help separate high-risk interactions from your primary identity, but not all secondary numbers provide meaningful privacy protection.
Many VoIP services retain extensive user metadata, often storing it for long periods in systems that may not be properly secured. If breached, subpoenaed, or sold to brokers, your “private” number becomes another permanent record tied to you, negating the privacy benefits it was meant to provide.
Secondary numbers from legacy telecom providers face the same problem—they're designed for permanence and tracking, not isolation. Conventional carriers routinely track network metadata and unique SIM identifiers, such as IMSI, for life, allowing them and third parties to monitor your location and behavior over time.
Real incidents highlight how exposed this ecosystem can be. In 2024, AT&T disclosed a massive data breach affecting nearly all its wireless customers, exposing call metadata and private details to hackers. Likewise, other major carriers, including T-Mobile, Verizon, and Mint Mobile, have repeatedly experienced large-scale breaches.
To reduce the exposure of your identity and metadata tied to your phone number, switch to Cape.
Cape’s Secondary Numbers are designed to reduce long-term exposure at the network layer without linking back to your primary identity. Additionally, these numbers are real cellular lines, which means they work more reliably with authentication systems and modern account verification flows than disposable VoIP numbers.
Cape: The Carrier Built for Security and Privacy
Cape is a privacy-first mobile carrier designed to keep your communications safe from surveillance and misuse. Unlike traditional cell phone plan providers, our business model centers around providing you with premium and secure call, text, and data, rather than harvesting and selling your information.
Our service is built from the ground up with privacy and security at its core, offering unique features like:
Privacy & Security Feature | Description |
Cape doesn’t ask for your name, address, or Social Security number. We only collect the information necessary to provide service, and we retain that information for the minimum amount of time possible. | |
Traditional carriers rely on a fixed International Mobile Subscriber ID (IMSI) to connect your device to cellular networks. This is a vulnerability that lets carriers, advertisers, and bad actors identify and track your device. Cape lets subscribers automatically rotate their IMSI every 24 hours, making it infinitely more difficult to track you or your device. | |
Many services ask for your phone number, but sharing it exposes you to spam, scammers, data brokers, and a variety of other risks. VoIPs, on the other hand, don’t work with 2FA, cost extra, and aren’t encrypted. With Cape, you get two free additional SMS/MMS lines that are middle-to-end encrypted. | |
Most U.S. carriers store your call and text metadata for years, sometimes indefinitely. Cape is built to forget, so call data records (CDRs) are deleted after just 24 hours. | |
Cape nullifies the threat of SIM swapping by completely removing humans from the loop. During signup, you receive a 24-word phrase that generates a private key tied to your number. This effectively means that no one (but you) can move your number to a new carrier or device, not even Cape. | |
Legacy network protocols, like SS7, leave you vulnerable to hackers that can track your location, intercept your calls and texts, and steal sensitive information. Cape’s Network Lock relies on a proprietary signaling proxy to verify that your device’s physical location matches the network it’s trying to attach to. If we detect anything out of the ordinary, Cape automatically blocks the connection, nullifying the potential threat. | |
Traditional voicemail systems are outdated, unencrypted, and another security hole bad actors can exploit to gain access to your sensitive information. Cape encrypts all voicemails, ensuring only you can access them. | |
While roaming, your phone connects to local telecom providers to enable service. But, who knows who might be listening on the other end. Cape provides you with peace of mind by routing your traffic through our U.S.-based mobile core, ensuring your identity, data, and communications remain private and secure. |
Ditch Legacy Carriers: Get Cape Today
Cape is a “Heavy” Mobile Virtual Network Operator (MVNO), meaning we own our mobile core and provision our own SIMs. This gives us full control over how accounts are authenticated and what data is collected (and for how long), and is how we are able to provide privacy and security features no other carrier on the market can offer.
Get started with Cape today and enjoy the peace of mind, knowing you are fully protected against scammers, hackers, bad actors, and other mobile threats.
To help protect more than just your phone, we’ve partnered with Proton. As a new Cape subscriber, you can choose between Proton Unlimited and Proton VPN Plus for just $1 for six months.
