An extension number is a short, usually 2–4 digit code assigned to each user, department, or phone in your organization’s phone system. It works like an “apartment number inside a larger building”—instead of dialing the main company number and waiting for a transfer, you can enter the extension to reach someone directly.

📌 When to Use an Extension Number

• Calling coworkers or departments internally
• Routing external callers to the right person quickly
• Setting up voicemail or call forwarding

✅ How to Dial an Extension

1. From inside your company phone system (desk phone, softphone, or mobile app):
• Dial the extension number (e.g., 102) and press Call.
• You’ll connect directly without dialing the full external number.
2. From outside the company (calling the main number):
• Dial your company’s main phone number (e.g., +1-555-123-4567).
• When the automated menu answers, enter the extension (e.g., 102).

🛠️ Prerequisites

• You need to know the extension number assigned to the person or department.
• Your system administrator sets the length (2–4 digits) and ensures extensions are unique.

⚠️ Limitations & Edge Cases

• External callers may need to wait for the greeting before entering an extension.
• Extensions only work inside your company’s PBX or VoIP system—you can’t dial them from unrelated phone networks without the main number.
• If two users have the same extension assigned (rare), calls may fail—contact your admin.

🎯 Expected Result

• If the extension is valid, your call connects directly.
• If it’s invalid, you may hear: “The extension you’ve dialed is not in service.”