[SR-Users] Simple Trunking with Kamailio

Ok, this is probably an easy question: Say I have my kamailio server set up and all of my voip clients are gleefully calling each other... but now I want to connect them to the PSTN. Can I set up kamailo to trunk calls using a few grandstream gateways? or is Asterisk neccesary? Sorry if the answers out there, but I haven't found anything that answered the question directly. I'm a linux admin, but I'm new to PBX's and the like. I've installed kamailio in the past using instructions specific to that situation, but haven't configured trunking (or I didn't recognize thats what it was) references to howtos or tutorials would also be greatly appreciated Thanks for your help, Jared Martin