A bit more playing with this thing, and I'm getting some weirdness...
On the web interface:
Physical Interfaces->Line Port->InboundCallRoute is set to {aa} and Default is unchecked.
Voice Services->SP Service->X_InboundCallRoute is set to {aa] and Default is unchecked.
On OBiTalk both are set to device default.
The Line port is doing well and consistently routing call after call to aa. I can dial my cell with **1 and get the caller id of the line hooked up to the line port. All is well.
SP1, on the other hand, reverts back to "ph" with Default checked within a few minutes of the re-boot. I can get one call in that works, and the next just rings.