Multiple Locations and phone lines

We are setup with 10 POTS lines in one location and 3 POTS in a second location. We want to allow either location while connected to be passed a line as needed. Has anyone done this with this software. I am reviewing the Xtreme 300 for our installation.

You will need a “tie-line” between the two locations, IAX2 is preferred as it stands for InterAsteriskeXchange Protocol(2), the WIKI covers it.