Asterisk Trunk

Hi ,

Following is my present setup

Provider -------->SIPSER based PBX------------>IP-Phone

the SIPSER bases PBX solution is a properitery solution and gives only limited web based access.

I plan to Use asterisk box as my primary PBX and use the existing SIPSER Box as a SIP Gateway.

Provider <-------->SIPSER<------------>Asterisk<-------->IP-Phone

I created a sip trunk from my asterisk box to the SIPSER .The Trunk got registered on the SIPSER .

However when I make the call using the SIP trunk I get a route busy message.The same is for Incomming calls

any ideas on what I might be missing