What Is the WhatsApp Calling API?

If you’ve been wondering what the WhatsApp Calling API is, the WhatsApp Calling API (also called WhatsApp Business Calling API / WhatsApp SIP Calling) is a feature of Meta’s WhatsApp Business Platform that lets customers place a voice call straight from the WhatsApp app to your business phone system — without ever needing to know a PSTN number.

So while customers used to be able to only chat with you on WhatsApp Business, now they can also tap the “Call” button in WhatsApp and get connected straight to your customer service, sales, or support team.

Technically speaking, the call is converted into a SIP call and forwarded to a PBX system such as 3CX / Cloud PBX, where it lands on an extension, IVR, ring group, or call queue — exactly like a normal phone call.

The Technology & Protocols Behind It #

So it’s not just a concept to you, here’s what’s happening “under the hood”:

Component	Details
Signaling	SIP (Session Initiation Protocol) over TLS
Media/Audio	SRTP (Secure RTP), with key exchange via SDES
Voice codec	OPUS
Default port	5061 (SIP over TLS)
Meta’s SIP host	wa.meta.vc
Trunk authentication	IP-based (not a regular username/password)
Configuration API	Meta Graph API (via the WhatsApp Business Platform / Cloud API)

Because both signaling and media are encrypted (TLS + SRTP), your PBX’s connection to the WhatsApp Calling API must have a public domain (FQDN) and a valid SSL certificate — a plain IP address isn’t enough.

Technical Flow of an Inbound Call #

Here’s the end-to-end technical flow that happens when a customer taps the Call button on WhatsApp:

1. The customer taps the Call button in your WhatsApp Business chat.
2. WhatsApp (via the Meta Cloud API) initiates the call as a SIP call to the SIP server you registered (your PBX’s FQDN), using the TLS port (usually 5061).
3. The SIP INVITE is received by the PBX (3CX) through the SIP Trunk configured specifically for that WhatsApp number.
4. Voice media is sent encrypted via SRTP, decoded with the OPUS codec.
5. The PBX processes the call just like any other SIP trunk call, then routes it based on the rules the admin has configured — to an Extension, Ring Group, Call Queue, IVR/Digital Receptionist, or even an AI Agent.
6. The call shows up as an inbound call in the agent’s 3CX Web Client, Desktop App, or IP Phone — the agent never needs to open the WhatsApp app at all.

Important note: as currently implemented, WhatsApp SIP Calling only supports inbound calls from WhatsApp to the PBX. Outbound calls still go through the regular SIP trunk/PSTN path.

What You Need Technically to Set It Up #

Before the WhatsApp Calling API can be turned on and connected to your PBX, there are a few technical prerequisites:

• A WhatsApp Business Application that’s already live on Meta for Developers, with active messaging permission for the business number you’ll be using.
• A Phone Number ID and User Access Token from your WhatsApp Business account (obtained when you set up WhatsApp Messaging in 3CX/the Meta Developer Portal).
• A public FQDN (domain) for your PBX, e.g. pbx-yourcompany.com, along with a valid SSL certificate.
• The SIP TLS port (5061) open on your firewall specifically for communication with Meta’s servers.
• A PBX system that supports custom SIP trunks, such as 3CX (a recent version with WhatsApp SIP Calling support).

High-Level Configuration Steps #

Broadly speaking, the activation process looks like this:

1. Enable the SIP feature on your WhatsApp Business number through the Meta Graph API — sending a request to enable the calling and sip status, while registering your PBX’s FQDN and port as the SIP destination.
2. Verify the configuration with a GET request to the Graph API to confirm the SIP status is ENABLED and Meta’s SIP credentials have been generated.
3. Turn on Call Settings in WhatsApp Business Manager: allow voice calls, allow callbacks, and show the Call button in chats.
4. Create a new SIP Trunk in 3CX — you can use the official WhatsApp template and simply import it, or configure it manually with:
   • Authentication Type: IP-based
   • Host: wa.meta.vc
   • Port: Auto discovery
   • Transport Protocol: TLS
   • SRTP Mode: Enforced
   • Codec: OPUS
5. Set the call destination (default destination) — whether calls go straight to an Extension, Ring Group, Call Queue, or IVR.

Once all these steps are complete, your business WhatsApp number automatically works as a SIP call source connected directly to your PBX.

How Is It Different from Regular WhatsApp Business? #

WhatsApp Business (App)	WhatsApp Calling API
Used manually from a single phone	Connected to a PBX system via SIP trunk
Calls can’t be recorded automatically	Can be recorded and included in reports
Can’t be routed into a queue/IVR	Can be routed to a Queue, IVR, or Ring Group
1 agent = 1 device	Many agents can take calls at the same time
No admin-managed SIP/SRTP encryption	Signaling & media are encrypted (TLS + SRTP)
Not integrated with a CRM	Can be integrated with a CRM and reporting

Why Does the WhatsApp Calling API Matter for a Business? #

• Customers are already used to WhatsApp — they open it more often than a phone dialer.
• Routes into Call Queues & IVR just like a normal office call (Support Queue, Sales Queue, Technical Helpdesk).
• Automatic call recording & monitoring, feeding straight into agent performance reports.
• Agents don’t need to log into WhatsApp — they can simply use the web client, softphone, or an IP Phone.
• One platform for every type of call: WhatsApp Voice Call, PSTN, SIP Trunk, and internal calls — all handled by the same PBX.

Who Is a Good Fit for the WhatsApp Calling API? #

• Hotels & Hospitality
• Clinics & Hospitals
• Logistics & Delivery
• E-Commerce
• Customer Support Centers / Call Centers

Security Notes & Common Troubleshooting #

• Since only port 5061 (TLS) is used and Meta’s host is wa.meta.vc, make sure your firewall whitelists this traffic specifically rather than opening the port broadly.
• Keep SRTP Enforced turned on — don’t disable it — so call media stays end-to-end encrypted between Meta and your PBX.
• If you have more than one WhatsApp Business number you want to enable SIP Calling for, each number needs its own separate WhatsApp Application on Meta for Developers — the setup process above has to be repeated per number.
• Make sure the Main Trunk number on the 3CX SIP Trunk used for WhatsApp Calling is different from the one used for the WhatsApp Messaging trunk, to avoid configuration conflicts.

Conclusion #

The WhatsApp Calling API is a modern way to bring voice calls from WhatsApp straight into your business phone system. Technically, it runs on SIP over TLS with SRTP + the OPUS codec for media, connecting through the Meta Graph API to a SIP Trunk on a PBX like 3CX — complete with queues, IVR, recording, and reporting, without replacing the PBX system you already have.

For businesses whose customers are more active on WhatsApp than on regular phone calls, this feature can be the most practical way to speed up response times while keeping every conversation neatly logged in a single dashboard.