[Belegorn]

Gondor

Orthanc-stone - Isengard, had a fixed orientation.
Arnor-stone = Minas Tirith, had a fixed orientation.
Ithil-stone = Minas Ithil, it was thought to be either lost or captured by Sauron. It had a fixed orientation.
Osgiliath-stone = Osgiliath, it was the master stone and could eavesdrop on 2 other stones in communion, other stones could not do this, they would just see the stones as blank. It was a big stone that could only be lifted by more than one man. It was lost in the waters when King Eldacar was attacked the the tower burned. It could be revolved and still see in any direction.

Arnor

Amon Sûl-stone = The chief stone of the North; it was the largest and most powerful stone, mainly used to communicate with Gondor. It had to be lifted by more than one man. It was lost at sea. It could be revolved and still see in any direction.
Elendil Stone = Emyn Beraid, was not used for communication, but rather to look to the West where even Eressëa could be seen.
Annúminas-stone = Annúminas, Fornost, was lost in the sea. It had a fixed orientation.