Early on in my current campaign my players were sent on a quest by a wizard friend of theirs, he gave them a sending stone so he could keep in contact with them. After that quest ended my players got a nice big downtime, 1 month. One of my players, who owns a tavern, asked to dedicate that downtime to finding some more sending stones, one for each player and the pairs to be held by the barkeep NPC she employs. I rolled on the tables in XGtE and got a price that they could afford.
Are there any unforeseen downsides in letting them spend all their money on sending stones? I know this effectively gives them party wide telekinesis but since they’re using this NPC as a telephone switchboard (literally how they pitched the idea) I can reserve the right to say he’s busy and can’t forward their messages.
I decided to give them the stones and then ran a session, they got separated for a few minutes and spent most of it talking through that npc to each other instead of trying to solve the problem that separated them. They’ve implemented a rule that he needs to write down what they say and relay the message exactly. 10/10 it was quite funny. Try doing this with your players.
Sounds like fun! I would reward the engagement with the stones they want. There’s room for all sorts of ways for it to work really well or really poorly. If they’re consistently using it to circumvent your story beats, maybe some interesting complications or particular defenses might be in order.