Question on linking 2 FreePBX box togheter

Here is my Setup, i have to PIAF box running, i have setup a IAX2 trunk to connect them togheter and it is working perfectly, but the problem is:
I need the users of the box #1 to be able to see if the users of the box #2 are online, ringing, or on the phone. and sme thing for the users of the box #2 they need to be able the see the BLF of te box #1. The 2 boxes are conected togheter via Hamachi VPN so the is no port blocked. I use Aastra57i phone for every user, i don’t know if i can put a BLFXFER key with let say [email protected] ip on the second box or something like that?? thanx for your help.