Here is my guide for setting up BLF (Busy Lamp Field) on asterisk 1.4 using a linksys SPA-942 voip phone. I must say that trying to find the right information took a little bit of time…In fact it took me about 2 hours to successfully set up the unused lines on my SPA942 to be used as indicators because I could not find enough detailed information in one location. Hence this post.

Asterisk does not easily work with shared line appearances unless the phones are made specifically for it. However, you should be able to get BLF working instead of SLA and have almost the same functionality. Below is what you will need to do to enable BLF on asterisk 1.4 using a linksys spa942 (this should also work on any Linksys/Sipura Phone that supports BLF and extended functions).

Edit your SIP.CONF file and enable these features (these MUST be enabled for hints to work correctly):

allowsubscribe=yes
limitonpeers=yes
notifyringing=yes
notifyhold=yes

In your SIP.CONF/USERS.CONF file, edit your users to contain the following code:

qualify=yes (im not sure this is necessary as I tested it without this setting and BLF still functioned correctly)
call-limit=100 (this can be anything, but 100 will keep you from denying any new calls)

In your EXTENSIONS.CONF file, you just have to enable hints by putting this in your default context (change the extension numbers with your extension numbers):

exten => 1000,hint,SIP/1000
exten => 2000,hint,SIP/2000
exten => 3000,hint,SIP/3000
exten => 4000,hint,SIP/4000

This enables BLF on your asterisk server. In order to configure your linksys spa-942, all you have to do is enter a few settings on the phone itself. But you must be sure you are currently running the newest version of the phones firmware (it is currently at 6.1.5(a)), BLF will not work without first running the newest firmware release! After you have confirmed this, use your web browser and enter the ip adrress of your phone. Click on admin login and then on advanced.

Under the Phone tab type the following:

Short Name: Anything you want to show up next to the LED to remind you which line it is you are monitoring.
Extended Function: fnc=blf+sd+cp;sub=5000@$PROXY;ext=5000@$PROXY

Above, I have two extensions; 5000 and 6000 which I am monitoring which show up on my phone line buttons 2 and 3. After these settings are entered, scroll down to Line Key Extended Function and enter these settings:

Server Type: Asterisk (*this is important!).

You do not have to enable line keys in the Ext. tabs  for this to work. Just click ‘submit all’ and wait for the phone to reboot. Youre done! Hopefully this will save someone lots of time searching google for consolidated information! If youre looking for more SPA-942’s you can get them for a decent price on ebay or here.