PROBLEM with SIP TRUNK BETWEEN 2 SERVERS

Hi all…
I have been trying configuration of sip trunk between two asterisk servers located with in a single LAN. I installed asterisk 1.6.2.16.1 on centos 5.5 linux. In server1 sip.conf is implemented as

[interboxsip2]
type=peer
host=192.168.1.4
context=callfromserver2
dtmfmode=rfc2833
disallow=all
allow=ulaw
allow=gsm
insecure=invite
[1000]
user=1000
secret=1000
type=peer
host = dynamic
context=internal
allow=all

and server 2 as
[interboxsip1]

type=peer
host=192.168.1.8
context=callfromserver1
dtmfmode=rfc2833
disallow=all
allow=ulaw
allow=alaw
allow=gsm
insecure=invite

[2000]
username=2000
type=peer
host=dynamic
context=phones
secret=abc123
allow=all

DIALPLAN of server1 as

[callfromserver2]

exten => _9xxxx.,1,NoOp()
exten => _9xxxx.,2,Dial(SIP/interboxsip2/${EXTEN},30)
exten => _9xxxx.,3,Hangup()

[internal]
exten => 1000,1,NoOp()
exten => 1000,2,Dial(SIP/1000,30)
exten => 1000,3,Hangup()

and server2 As

[callfromserver1]

exten => _8xxxx.,1,NoOp()
exten => _8xxxx.,2,Dial(SIP/interboxsip1/${EXTEN},30)
exten => _8xxxx.,3,Hangup()

[phones]
exten => 2000,1,NoOp()
exten => 2000,2,Dial(SIP/2000,30)
exten => 2000,3,Hangup()

But its not working
can anyone help me out…