Communication between two people at different locations, is difficult. If you don't have or don't want to lose a radio, it can be a pain in the ass. But what I am most worried about is locating a person. You can find they say that they are up in one location which means something to you, but means something else to him. This can render location seeking as "annoying as hell". So what I am suggesting to overcome this problem is to add signal flares.
My Thought And Plans For Signal Flares:
They can be built by Scientists and are one time usage for lighting up to 30 seconds - 1 minute depending on you.
They are used up like grenades, you equip them, left click will at first ignite the flare, then left click will throw the flare (it might be possible to burn zombies and what not with it?) and right click will drop it, similiar to a grenade.
The cost of this 1 time usage item could be 5-2-10, as previously mentioned, built by scientists.
They could have a programmable colour to distinct person to person and it may also be signals between people. A red flare could signal a person to attack, blue to stand down, but that is all up to the player.
They would also be very helpful in darker maps where you have little to no light, though expensive so therefore should have a brighter colour on dark maps.
Thank You for reading this, I do hope in all sincerity you will think about this atleast.
-Silence The Mutant Redneck