I have a scenario, where a customer wants to use AT&T SIP trunks. They already have an MPLS in place, so AT&T is suggesting IPFlex over the MPLS to deliver the SIP trunks. They said either an SBC is needed between 3CX and the AT&T router or 3CX must act as an SBC to terminate the connection. Has anyone run into this scenario? I am just trying to avoid any issues or caveats. If an SBC is required, I'm thinking an AT&T provided and managed one would be the best option.