I want the following setup:

1 Kamailio server to handle internal calls (A/V), IM and Presence.

1 Asterisk or any other way to communicate with an NGN where I will create the SIP Trunk to route calls outside of the network.

Is this the right approach or there is a way to directly communicate with the NGN to make a SIP trunk by using some external modules. 

Any guidelines will be highly appreciated.

Rizwan Khan