Those with a Fluctuating Signal...
Try this: Wipe your phone clean (under Security Options) and leave Wi-Fi off. Or simply turn off your Wi-Fi.
I'm not sure if it was certain 3rd party software or the Wi-Fi that was making my signal fluctuate (0 bars to visible bars) constantly leading to more dropped/missed calls.
Yeah I know it's pretty ridiculous having to set Wi-Fi off but it worked for me, so far. I've being keeping an eye on my phone for that last few hours and my phone hasn't seen 0 bars since I restored and leaving Wi-Fi off.