Get a Quintum A200. Connect the FXO ports to old Ma Bell line (248) XXX-XXXX. Make the A200 register with the A800 as a gatekeeper.Enable IVR on the A200. It is very basic, but it works.
When someone rings your line in Michigan, the IVR ask for the PIN. If you enter the PIN (you need to set the pin on the A200), you get a second dial tone.You dial the number set on one of the ports of the A800, and bingo.
If you want the system to work without PIN, meaning soeone will call that number and will ring somewhere in Asia,you need more work.
I sugest calling Quintum support and they will give you the steps.
Good luck.