I think you've just described the PhoneGnome -- the iPod of telephony!

PhoneGnome is in many respects a neat device. But it doesn't fit the bill for a very simple reason. It knows about PSTN call activities only as seen at the interface. But SCP has access to much wider set of information.

In another respect, the current version of PhoneGnome is restricted in conveying the information to the user because it uses the FXS port and so can not deliver richer signaling information.