Please be aware that you are not communicating with Apple when you post in these forums. The only people who will reply to your posts are your fellow users.
That someone told you that the iPhone 4 can't handle the work load is just nonsense. We have a number of users using the iPhone 4 extensively on a daily basis with no problems. Why you have had so many issues I can't say; it could be your environment, your usage, or just bad luck. I have no way of determining.
Assuming that after dropping the iPhone and smashing the screen you had it replaced by Apple and did not have some unauthorized service center repair it, then I would suggest you call Apple Support for the UK, ask to speak with someone in Customer Relations, and explain the continuing problems to them. There may be something they can do for you.