Wondrous item, uncommon, requires attunement

A smooth, flat stone that fits comfortably in the palm of your hand. Carved designs decorate its surface.

Over the course of an hour, you can attune to the stone, imbuing it with a unique magical pattern that corresponds with your soul. If another creature has a sending stone that they have attuned to, and you hold your sending stone to theirs for 6 seconds, the stones exchange and store each-other's unique magical patterns. As an action while holding the stone, you can attempt to establish contact with any sending stones your stone has previously exchanged patterns with. The target stone will begin to vibrate, chime, flash, or behave in some way to get the recipient user's attention, and once they notice, they can hold the stone and complete the contact using their reaction. Once contact is established, the users of the connected stones can converse freely with one another, either through mental messages by being in physical contact with the stone, or by the stones themselves receiving and emitting sounds. The connection can be ended as a bonus action by either user.

Once a sending stone's attunement ends, it loses all magical patterns of the other sending stones it has stored. However, if you spend an hour to voluntarily end the attunement on the stone, you can have it keep it's stored patterns for the next creature to use when they attune to it.

Sending stones can normally establish contact across planes, but this can fail if there is sufficient magical interference between the sender and recipient.