This is just my opinion. Feel free to argue with me!
There seems to be a lot of confusion concerning the walkie talkie. A lot of people on this board seem to think that the person on the other end is either A) Clem's Dad or connected to her Dad in someway - B) Connected to Glenn or - C) been talking to Clem ever since Macon.
A - Clem's dead is either dead or a walker. He was attacked by a strange man outside of the hotel. The same hotel the group is currently headed towards.
B - I really don't see how this is possible unless Glenn ran into a another group and somehow gave or lost the radio. Then this person or group made their way to Savannah before Clem's group did. A long way with a lot of zombies in between. This has to be the least likely scenario.
C - MOST radios like this do not have that long of a range. It's about 130 miles or so from Macon to Savannah. It would be a stretch to think that Clem found a radio and another person in Savannah just happened to another radio with that type of range. And, they happened to be on at the same time. Possible, but unlikely.
Solution, IMO: Clem started using the radio the closer she got to Savannah in the hopes her parents would have the other one. Remember though, she had one in the tree house, and Lee used the other in the kitchen. Glenn took that one. (See B above.)
Clem, being young, alone, and afraid probably started clicking on the radio and asking for her Mom and Dad - just like she did in the tree house back home. She probably heard nothing at first, but then someone in Savannah was scanning - maybe with a HAM radio or something. The stars aligned and this pervert or another group of bandits heard her and is pretending to know the whereabouts of her parents - thinking Clem's group is loaded with supplies.
Either way, I just don't see any type of happy ending for the group in Savannah. Maybe Huey's on River Street is open and they can get some Shrimp n Grits!
Of course, we could all be wrong.