I have sprint and have both devices
The sgs3 has worse call quality but holds on to calls better, so less drops
The sgs4 has better call quality, but can't really hold on to calls as well resulting in a lot more dropped calls
I also notice my sgs4 will randomly lose data signal and take minutes to find one again while my sgs3 holds on and doesn't lose data. In the rare instance it does, it finds the data connection again within 10 seconds
Sent from my SPH-L720 using Tapatalk 2