Service providers such as ISPs, MSPs, ITSPs target a large number of remote users and need to have an easy and centralized way to deploy their solutions. In the past, in order to deliver hosted PBX or SIP trunk services, the customers' router or firewall had to be configured with port forward rules. In many cases the customer was forced to obtain a Public static IP address. This becomes a major problem as many customers do not want to change their network or are too small (SMB or SoHo) for the Service provider to spend the time getting customer's routers ready. In many cases the customer is on the go and uses hotel, airport or public networks and does not have any control over the router that connects him to the Internet. With NatPass SBC there is no need to modify customers' router or Firewall, service providers ship configured SIP endpoints and once they are connected VoIP just works.
See most common causes for NAT traversal issues:
Multiple internal SIP devices
Restricted Cone or Symmetric NAT
Static Public IP not available