Patapsco have two solutions for sharing and contending ISDN PRIs:

Liberator “S” supports up to 3 PRIs in a single unit.

Liberator “D” supports up to 4 PRIs in a unit and multiple units can be connected together in a non-blocking architecture to provide 8, 12, 16 etc PRIs. Additionally these units can be located around a building, delivering the ports where they are needed.