A VPN gateway for interfacing two or more VPNs to external networks such as the internet or a PSTN having different addressing schemes, has a NAT shared by the VPNs for converting VPN addresses to addresses of the external network. An advantage of this is reduced number of additional network elements, e.g. boxes, and fewer additional addresses. The NAT can be a source and destination NAT, arranged such that entities in the external networks appear to have an address within an address range of the respective VPN. Thus, entities in the external resource can appear as trusted resources inside the VPN. The gateway can incorporate a converter for converting between formats such as VoIP packets and TDM calls.