A scenario occurred to me whereby the mysterious voice over Clem's walkie-talkie is entirely benevolent (albeit on the suspicious side). I'll leave interested readers to fill in a few blanks.
Clem's dad was injured. Clem's mom brought the dad to the hospital in Savannah. Mystery Voice was a nurse at the hosptial, and his hobby is shortwave radio (heck, why not). In tending to Clem's dad MV becomes friendly with both parents. The mom in particular confides their dilemna. Her husband is ill and their child is back in Macon, ostensibly under the care of a babysitter, but as the night progresses it becomes clear that all hell is breaking loose throughout the region, so mom gets more than desperate enough to discuss things with a stranger. Clem's mom mentions the walkie-talkie and shows her wt to MV who says, 'aha, that won't reach Macon, but I know how to boost the signal, if that'll help, and how to pick up weak signals at long distances'. As the ZA worsens, the nurse/ham radio operator gets seperated from Clem mere et pere, and out of concern for their little girl attempts to contact her through his shortwave equipment. He's holed up in his apartment and as he begins to talk with Clem learns that she's currently with a middling sized group of armed, angry people who sometimes hit each other.
Now, if you're MV, wouldn't you want to reunite Clem with her parents, but without exposing yourself to this armed group unnecessarily? Wouldn't you rather take a look at them first without revealing yourself? One way to do that is to stay in touch with Clem but without revealing yourself to this Lee character, and that homeless guy she mentioned. The obvious way to do that is to ask Clem to keep your conversations with her a secret for the time being. Also, given that you'd be able to tell Clem some specifics about her parents, you'd be able to prove to her that you knew them. Plus, Clem also thinks that just maybe one of the people in her group shot a kid. It happened out in the woods so she's nor sure. Also, this Lee guy cut Clem's hair. What kind of weirdo gives haircuts during the ZA?
Far better to conceal your identity and location until you get a look at this odd bunch--before revealing yourself and before leading them to Clem's parents whom you like and who may be very vulnerable if they're even still alive--than blindly give out too much information to armed adults you don't know but who sound pretty darned sketchy.