When you use the 3CX Admin console and setup BLF under the extension, the BLFs are ONLY setup if you have the Attendant Console SPA500S added onto the phone.
To get the BLFs to work on 1 of the 12 extensions on the Cisco 509g or any of the other Cisco SPA5xx phones do this:
1. Go to Phone tab.
2. Select an extension where you want to add a BLF.
3. Set Extension to Disabled.
4. Set Shared Call Appearance to Private
5. Under extended function enter: fnc=sd+blf+cp;sub=xxx@PBXIPADDRESS;ext=xxx
where:
You can enter all 3 of the below or just 1 or any combo:
sd=speed dial
blf-busy lamp field
cp=call pickup
sub=xxx and ext=xxx = the extension number
PBXIPADDRESS=the IP of your 3CX Server
If you want to setup a call park, just enter SP0, SP1, SP2, etc to SP9 instead of the extension # under sub & ext for call parking.
Hope this helps. It's not clearly explained anywhere.