I'm considering utilizing Bandwidth.com for SIP trunking along with my existing Mitel 3300 system. Bandwidth.com is insisting on either a Public IP on the PBX, or an Edgemark or Ingate SIP ALG for NAT traversal. Doesn't IOS (I'm using a 2821 router) support SIP traversal through NAT? Is this where the Session Border Controller (SBC) configuration comes into play? I'm trying to keep this setup simple (fewer devices the better). I'm interrested to know your thoughts.