Just as an update, I thought I'd explain why I was asking.
I have a customer with 45 5312 phones, and loudspeaker paging. This customer also has several parking positions programmed.
We were experiencing an issue, where if a caller was parked, they would hear any and all pages. I was desperately looking for a solution, and while 45 is > 30, when they would page, it wasn't spiking the processor too much and support felt I should have been fine.
Been working on this for the last 3+ weeks.
Finally by re-building the page zone device by device, and making a page after each addition, we found our problem.
Turns out that one of the phones had used FAC 313 so they could listen to the MOH at their desk. Apparently (support isn't sure if this is by design, a bug, or an unintended consequence of having the pages programmed on a phantom SL-8, on a phantom DEI at this point), but by this one user having "Background Music" enabled, it was binding the MOH and Paging audio paths together. As long as this users phone was either offline or not in the page zone, everything worked correctly.
Just wanted to put this out there in case anyone else is seeing this at all.
FYI, this customer is running rel 6.