Mich. Comp. Laws § 484.1204: System designs.

Sec. 204.

A 9-1-1 system implemented pursuant to this act shall be designed to meet the individual circumstances of each county and the public agencies participating in the 9-1-1 system, and shall be within the service limitations of service suppliers providing the 9-1-1 service in the 9-1-1 system. System designs shall include provision for expansion of the system to include capabilities not required in initial implementation, including the addition of PSAPs and secondary PSAPs.

Every 9-1-1 system shall be designed so that a 9-1-1 call is processed by means of either the direct dispatch method, the relay method, or the transfer method. At least 2 of the specified methods shall be available for use by the PSAP receiving the call. The PSAP may handle nonemergency calls by referring the caller to another number.