SIP Trunks can work with a SIP-ready PBX. SIP Trunks can also be made to work with traditional analog or key systems with an IAD (Integrated Access Device). The SIP Trunk service provider will need to interoperate with the underlying equipment manufacturer. However, it should be noted that with the advent of standards around RFC and SIP Connect, the challenge of finding SIP Trunk Service Providers with SIP Trunk compatible equipment is significantly decreased.