Question about ISDN Lines

Hi, we have an asterisk server with 10 extensions and 1 PCI ISDN CARD (ISDN standard 2 channels, multinumber: 7 numbers)

Now we have a question: on our incoming rules set we have that if somebody is calling a specific number a specific extension is called.

On the phone (a linksys SPA962) we have the led flashing and it’s ok, and when the user answer the phone on his phone the light become red fixed until the conversation is on.

Question is: we’d like other users to see that 1st channel of ISDN is busy.

Considering that we even have 3 trunk SIP for others channel, should be wonderful if on linksys phone we could see status of all lines, ISDN or SIP

maybe we have to work with shared extensions, but we did not exactly understand how to work with them