I'm having a similar problem to this Samsung Galaxy S4 Call Drop and Network Issues thread.
- signal randomly drops from full bars to nothing/nil
- however it isn't random when connecting to a wifi network (cell connection drops completely every time)
- this doesn't happen when using 2g only
Phone model = SGH-1337M
Running Jamal2367's 4.4.2 GPE ROM
Baseband version = 1337MVLUAMG1
Build number = KOT49H.S001.131204
Any help is greatly appreciated!