You may also use FXS/FXO voip circuits such as MultiTech if you can't afford two new systwms.
Can be used on any phone system (just about).
Basically you would have pool key for second system. Press button you get ICM tone from Wash. Dial an ext,
dial a trunk code to make a local call in Wash. or dial a page code and page the other campus. transfer calls etc. Works same on other end.
Not seamless but works. Low cost