Grandstream GXP 2000

Hello All,
I am looking for information on the following:
I am on AsteriskNow Beta 6
I have 10 Grandstream GXP 2000 IP sets, all working and box is in production mode.

My question is:

When a call is placed on hold on one of the Grandstream sets it lights the flashing lamp until the call is taken off hold.
Is there a way to cause all other 9 Grandstream sets to have the same flashing hold indication for the same held call at the same time? The objective being to be able to pick up the call from any other set? I already have call parking built and it is working as specified. The customer does not want to use call parking. They want use hold key functions.
Any information woulld be appreciated.

Look up the Shared Line Appearance feature.

Thanks dufus,
Information was very helpful but still need info.
I am closing this post and re framing my question.
thanks again