Hi Brian,
The application is simple... notify me when my physical mail has been delivered. I used to use an eagle-eye wireless to do this, and via ActiveHome i triggered a sound and sent myself a text. But, in this house my mailbox is (way) out of range of the wireless. So, I thought I would just run a wire to the PF284. I guess the simple answer to your question is I just need a dry contact sensor. I just looked at the Insteon as you said, and it looks right, but can it interface with X10?
Cheers