I am using two Grandstream GXP-2000 phones (a 4 line phone) with elastix. I have them each setup as their own extension. I have a ring group setup so that if a call comes in, it will ring both extensions. The phones are working fine except that if I am on a call and another call comes in, the call will only ring on the open extension (not the one I am using). How can I get the call to ring on the second, third, etc. line of my extension even if I am in a call? Thanks.