Any other similar spells?

[Opuk0]

Looking through some spells, I've found 3 spells that seem incredibly similar. Those being;

Shield Speech
Silent Table
Zone of Silence

[avr]

There's message for the cantrip version, and various forms of telepathy for the higher levels. Secret speech, hidden speech and codespeak are related too.

Hidden communication is clearly a frequently (if secretly) researched topic where the wheel is reinvented on a regular basis.

[Opuk0]

Yeah seems there's a lot of that with Pathfinder

[Coidzor]

Telepathic Bond serves a similar function.

Add in Permanency if you've got a dedicated group going.

The Teamwork Feat Bonded Mind also would be applicable I believe.