Direct "Talkaround" communication would have to be a hardware change. The system is set up for duplex operation. Tx & Rx are split by 45 MHz (825 -ish and 870's.
It would need to have a broadband (usually the) transmitter, to spread a 45MHz jump. The duplexer would have to be switched in & out,
or another transmitter/similar means, if you want to use it as a two-way (bypassing the cell-sites completely).
Otherwise, one would have to rely on the system to have the "direct-connect" type operation.
(Let's see, what can be used for a PTT?)
Lastly, a "no minutes charged for subscriber to subscriber calls" (like some other plans). Then just set up a conference call/3+ way calling. As long as you're within the system coverage.
..........................................
Edit:
.--. --- ... - -. ..- -- -... . .-. .---- ----- ----- .---- --..-- ..-. .. -. .- .-.. .-.. -.-- -.-.--
My 1001'st post! The five stars didn't show at 1000 (Whatever five stars do..) Hmmm 6? months... Yeah I blab too much!
*****