[Serusers] Can SER do this?

I have a problem that I *think* SER can help with, but looking through the docs and samples, I don't see anything quite like what I need to do. Here's my situation: I have an Asterisk box setup internally with a few PSTN trunks. We have another box in a colo that we're using to communicate to a SIP trunk from bandwidth.com. Currently we have Asterisk running there, too. What we want to do is: * Have all outbound calls from Asterisk go to the SIP trunk at the colo. We have this working now using Asterisk at the colo. * Have all incoming calls from the SIP trunk (it has several DID numbers) be routed to the internal Asterisk box just like the existing PSTN trunks. I haven't been able to get this part working using Asterisk (which is why I'm looking at SER now) There is NAT involved between the colo server and bandwidth.com. Is this possible?