I need to purchase a Voice Gateway for a new Switchvox IP PBX system that will be connected to PSTN and a SIP trunk. Our network is primarly administered by an outside vendor that is a Cisco dealer so I would want the unit to be Cisco. This will be replacing a PIX 515 and also needs to handle Firewall and VPN needs for our network. I will be getting the vendors recomendation but I would like to do enough research to understand that what they propose is right for us and be able to ask questions. So I am interested in getting suggestions on what you would suggest is the best Cisco Voice Gateway model for my needs and why.