I'm sad to hear of the dilemma being faced by these users. 
Traditionally, the best fix for a phone acting up is the trusted battery pull, where you remove the battery while the phone is powered on then replace it. This clears out the cache and gets rid of a lot of junk that could be hindering the operation of the phone. Many of you have tried that to no avail.
The next step I usually recommend is to reinstall the OS to the phone. Over time, many factors can affect the OS and putting a new OS in (or reinstalling the existing one) often irons out these problems. Many of you have also tried that to no avail.
If a user ever finds himself/herself at this point, I usually recommend returning the phone to your carrier. If it's anything that can't be resolved by the first two solutions, it's usually a serious defect that needs to be addressed by your carrier through warranty work. Obviously, if your phone is older than one year old and is out of warranty, this might not be the best option. You would probably want to look into getting another phone, perhaps second-hand.
I might not have offered a viable solution but hopefully I've shed some light on appropriate steps to take in the future. 
