This page has some undocumented information on the Panasonic KX-TA hybrid PBX/key systems.
The Panasonic KX-TA308, KX-TA616, and KX-TA624 are small, out-of-production hybrid PBX/key systems that have an undocumented command-line control interface available through the serial port if you have a new enough unit. This interface is used by the commercial Programmator software [dead link removed], but it can be used manually as well, or with the Perl scripts that I've written for batch upload and download.
A KX-TA624 unit as sold in the US does not provide automatic route selection features... or, rather, they cannot be accessed by programming the system from the manager's phone. However, you can use the CLI to enable these features on a US unit. Here's an example of using an AT&T prepaid calling card for long-distance calls while sending local calls directly.