What is BLF?
Busy Lamp Field (BLF) is a feature that lets you monitor the status of other extensions directly from your phone. LED lights next to programmed buttons show whether colleagues are available, busy, or their phone is ringing.
Key benefits of BLF:
- See colleague availability at a glance
- Transfer calls with one button press
- Pick up ringing calls for other extensions
- Speed dial frequently contacted extensions
Identify extensions to monitor
Before configuring BLF, note the extension numbers you want to monitor. You only need the Extension Alias (the 4-digit number like 1001, 1002, etc.).
Locate the extensions in your portal:
Configure line keys
Access your phone's web interface and navigate to Dsskey > Line Key:
Line key configuration
Line Key 1 is typically already configured as your phone's own extension. Configure additional keys for BLF monitoring:
- Type — Select BLF
- Value — Enter the extension number to monitor (e.g., 1002)
- Label — Enter a descriptive name (e.g., "Reception")
Click Confirm to save the changes.
Understanding LED indicators
Once configured, the LEDs next to each BLF key indicate the extension status:
- Green light — Extension is idle and available
- Solid red light — Extension is busy on a call
- Blinking red light — Extension is ringing
- No light — Extension is offline or unregistered
Using BLF features
Quick transfer
While on a call, press a green BLF button to instantly transfer the call to that extension.
Directed call pickup
When you see a blinking red BLF light, press that button to answer the call ringing at that extension.
Speed dial
When not on a call, press any BLF button to instantly dial that extension.
Status monitoring
See at a glance who's available before transferring calls or walking to their desk.
Troubleshooting
BLF lights not working
Ensure both phones are registered and online. Check that the extension number in the Value field is correct.
Can't pick up calls
Directed call pickup may need to be enabled in your PBX settings. Contact support if this feature isn't working.
Wrong extension monitored
Double-check the Value field contains only the 4-digit extension number with no prefixes or extra characters.
Model-specific information
Different Yealink models have different numbers of line keys:
- T46S/G: 10 line keys
- T48S/G: 16 line keys
- T54W: 10 line keys + USB expansion
- T57W: 16 line keys + USB expansion
Expansion modules like EXP50 and EXP40 can add additional BLF keys for larger teams.