Telepathy allows two way communication. It is not explicitly specified if the non-telepath can initiate, but if we make the (reasonable) inference that the kalashtar is always "listening" such as our ears are, so that a non-kalashtar can telepathically attempt to call out.
"a non-kalashtar can telepathically attempt to call out"
Non-kalashtars do not have telepathic abilities. By allowing them to "telepathically call out", you are giving telepathic abilities to a non-telepathic race.
The Group Mind feat gives this, but why should non-kalashtars get it for free?
The kalashtar might be "telepathically listening", but without a telepathic transmitter, how does the non-kalashtar dial the call?
The purpose of Group Mind is not just to allow non-kalashtar PC 1 to communicate with non-kalashtar PC 2 without the kalashtar PC filtering the message and to allow simulataneous communication, it is also to allow non-kalashtar PC 1 to telepathically communicate in the first place ("
Any ally within the range of your telepathy can communicate", not just the kalashtar). By giving the non-kalashtar PC a telepathic mouth with which to dial the call for free, you are giving the most important part of this feat to the non-kalashtar PCs in the party and invalidating most of the utility of the feat.
A kalashtar without the feat can totally emulate most aspects of the feat by just saying "go ahead guys, I'll forward your messages". Why have the feat if the kalashtar PC basically gets it for free anyway. Nobody would take the feat.