I'm afraid that yours/ours problems with ghost calls aren't solved with the above mentioned workarounds.
1. I never use the LG Application Manager to kill apps, or any other Task Killer.
2. I always set the network connectivity to GSM-only or HSPA-only, and I still receive ghost calls like many other users who reported that they still get ghost calls on 2G-only mode.
3. I'm afraid 4-days are not enough to confirm if you still have the problem. The ghost calls frequency and appearance are completely random. I call my O3D (with stock GB ROM, unrooted) from my second phone 5-10 times a day. There were times that I didn't have ghost calls for 10+ days, then I had them for 1-2 days, then no ghost calls for 5-10 days and so on.
WRT #2 - I set the GSM/HSPA Auto mode....not the GSM-only or HSPA-only modes.
WRT #3 - I did not see the ghost calls / txt issue at all in 8 days on the 2Degrees cellco...and now it's 5 days back on Telecom without any ghost calls. If you wanted to combine those, it's been a total of 13 days without the problem at all.
The only other thing I did that could have had any impact was a factory reset before going to the 2Degrees SIM....but I had the ghost call issue several times in the day following the factory reset, which was why I decided to switch telcos to test that. Maybe it cleared something out, combined with swapping SIMs.
I know that being on Bell Canada for a couple of months saw Bell 'soft-lock' my phone and I had to use the SIM Toolkit to manually reset the network. Perhaps the factory reset cleared some persistent setting somewhere picked up from a network I was on at some point. I am speculating. I don't know.
Whatever may have changed, I was seeing the problem 4-5 times day at least until swapping to 2Degrees....and haven't seen at all, even after swapping back to Telecom. The only other consistent change was setting the phone on GSM/HSPA Auto.
Maybe my telco fixed something broken in their network. I can't rule that out either.