[Asterisk-Users] Interfacing AT&T Spirit System to Asterisk

[Matt]

Greetings,
Does anyone know if there is a cost effective way to interface an
older AT&T Spirit system into Asterisk.
I'm only interested in A) being able to offer voicemail and B)
possibly an AAT to callers.
I've thought about just stringing the FXO cards into the line1/2 slots
that go into the Spirit system... asterisk would pickup if no one
answered the Spirit phones....

however....

Is there anyway anyone knows of to either A) allow transfer between
the two systems or... (I have 3 available PSTN jacks on the Spirit)
put an ATA on the asterisk which could go into line3 of the Spirit and
ring an extension (instead of the regular 4 phone call ring plan...)..
as far as I know the Spirit can't do DID.