What is number masking?
Number masking, also called call masking or anonymous calling, lets two people talk by phone or text without either one seeing the other's real number. Each side dials or messages a temporary proxy number, and a platform connects them in the middle. When the job is over, the proxy number stops working for that pair.
You have probably used it without noticing: a delivery rider calls you about your order, a ride driver phones you at the pickup point, or a landlord and a tenant exchange messages through an app. In each case the platform wants the people to be able to talk, but not to keep each other's personal numbers. This guide explains how it works, where it is used, what to plan for and how to build it. The technology sits on top of virtual numbers and the voice API.
How number masking works
- A session is created. Your app tells the platform which two real numbers should be able to talk, and for how long.
- A masked number is assigned. The platform picks one from a pool and stores the mapping.
- Each side contacts the masked number. The customer and the rider both see the same masked number in your app or a message.
- The platform bridges the call. It recognises who is calling, looks up the mapping and dials the other party, showing the masked number as caller ID.
- The session ends. Your app closes it, the mapping is deleted and the number returns to the pool.
The same idea works for texts. A message sent to the masked number is forwarded to the other person, so conversations stay on the platform. The calls themselves are usually carried over SIP connections, as explained in our guide to voice over IP.
Where number masking is used
| Industry | Who talks to whom | Why masking helps |
|---|---|---|
| Food and grocery delivery | Customer and rider | Keeps personal numbers private, ends access when the order is done |
| Ride hailing and mobility | Passenger and driver | Protects both, and keeps contact inside the service |
| Marketplaces and classifieds | Buyer and seller | Prevents taking deals off-platform, and allows dispute review |
| Home services and gig work | Customer and professional | Stops private contact after one job |
| Healthcare and telemedicine | Patient and clinician | Protects personal numbers and supports record-keeping |
| Real estate and travel | Agent, host and guest | Lets people coordinate without sharing numbers |
| Dating and social apps | Two members | Limits harassment and protects identity |
See our solutions for logistics, e-commerce, healthcare and travel for related use cases.
Benefits of number masking
- Privacy. Customers and workers do not receive each other's personal numbers.
- Safety. A harassing contact can be cut off by closing the session, without changing anyone's real number.
- Platform protection. Contact stays inside the service, which protects your commission and your data.
- Better service. Calls can be logged, timed and, where lawful, recorded to resolve disputes.
- Fewer unwanted calls later. After the order, nobody can call the old number to ask for repeat business.
Masking is a privacy feature, not a loophole. Tell people their calls go through a platform number and what is recorded. Transparency builds trust and is often a legal requirement.
Masked numbers vs normal calling
| Direct calling | Number masking | |
|---|---|---|
| Numbers visible to the other party | Yes | No, only the proxy |
| Control after the job ends | None | Mapping expires |
| Call logs and quality data | Held by the carriers | Available to your platform |
| Off-platform contact risk | High | Low |
| Set-up effort | None | An API integration and a number pool |
| Extra cost | None | Number rental plus call charges |
How to implement number masking
Create a session
POST /v1/masking/sessions
{
"parties": [
{ "role": "customer", "number": "+919812345678" },
{ "role": "rider", "number": "+919876543210" }
],
"expires_in": 3600,
"channels": ["voice", "sms"],
"reference": "order_4821"
}{
"session_id": "mask_77a1",
"masked_number": "+918012345678",
"expires_at": "2026-10-29T12:30:00Z"
}The calls above are illustrative; exact fields are in the API reference. Show the masked number in your app, and use webhooks to learn when calls start, are answered and end, so you can update the order screen and the customer record.
Plan the number pool
You do not need one masked number per person. A masked number can be shared across many sessions as long as no two active sessions with the same participant overlap, because the platform identifies the caller by their real number and picks the right mapping. A larger pool helps if one rider is on several jobs at the same time, or if a customer places many orders in an evening. Size it from your peak number of simultaneous sessions, and monitor how often the pool is close to full.
What to plan for
| Area | What to decide |
|---|---|
| Session length | How long after delivery should a call still connect? Many services allow a short grace period. |
| Caller ID shown | The masked number, so people recognise a service call |
| Recording and consent | Whether to record, how to notify, how long to keep it, and local rules; see compliance |
| Fallback | What a caller hears if the session has expired or the other person does not answer |
| Fraud and abuse | Limits on call volume, blocking abusive users and watching for unusual patterns |
| Data protection | Store mappings and logs only as long as needed; see our privacy policy |
Calls and texts that cross borders follow the rules of each country, and in India voice and messaging rules apply to platforms that make outbound calls. Our country rules guide lists the main points, and click-to-call is a related building block when the call starts from a web page.
Masking, privacy law and trust
Masking supports the principle of data minimisation, which says that people should receive only the personal data they need. Under privacy laws such as the GDPR and India's data protection rules, a phone number is personal data, and a service that hands it to every counterpart creates avoidable risk. Masking reduces that risk, but it does not remove your duties: you still hold the mapping and the call logs, so you need a clear purpose, a retention period and a way to delete them on request.
Trust is the other half. People are more willing to give their number to an app, and to take a call from a stranger, when they know the number will not be passed around. Say so in your onboarding and in the message that shares the masked number, and keep the promise by expiring sessions promptly.
Testing masked calls before launch
- Create a test session with two phones you control and place calls in both directions.
- Check what each side sees as caller ID.
- Let the session expire and confirm the number no longer connects.
- Test texts as well as calls, if you use both.
- Place two overlapping sessions for the same person and check the right one is picked.
- Simulate busy and unanswered calls to confirm the fallback message.
Good masking is invisible when it works: the call connects, and nobody learns more than they need to.
Add masked calling to your app. We provide the numbers, the API and the routing for delivery, ride and marketplace services.
Frequently asked questions
What is number masking?
Number masking, also called call masking, replaces real phone numbers with a temporary proxy number. Two people can call or text each other through it without either seeing the other's real number.
How does call masking work?
A platform assigns a masked number and maps it to both real numbers. When one party dials it, the platform recognises the caller, looks up the mapping and connects the call to the other party.
Why use number masking?
It protects privacy, prevents customers and workers from taking business off the platform, reduces harassment and lets the business log and control communication.
Can number masking be used for SMS?
Yes. Text messages sent to the masked number are forwarded to the other party, with the sender shown as the masked number. Content can be logged or filtered if you need to.
Is number masking legal?
Generally yes, and often encouraged for privacy, but call recording, consent, data retention and number-use rules vary by country. Tell users what is recorded and keep to local telecom law.
How many masked numbers do I need?
Enough that each active session has a distinct pairing. Many systems reuse one masked number across many sessions as long as no two sessions with the same participant overlap, which keeps the pool small.
What happens when a session ends?
The mapping is removed, so the masked number no longer connects those two people. Calls to it are rejected, sent to a message or routed elsewhere.