iMessage severe issues

After reading many discussions about imessage and finding almost no permanent solutions I have to ask again. My phone is a 16gb 4s on att, and throughtout the course of having my first phone i noticed many issues pertaining to imessage, what would happen is I would send a text or so i thought but it will either take nearly 15 minutes to send or it simply wont send at all. After several visits to my local apple store all they told me was to try and reset my phone as a new phone and back up all my personal info after it had been restored. This however worked for maybe 10 minutes before my phone was back to the same way it was before and so I called apple support and they told me i could either try resetting again or they would send me a new 4s. So i went ahead and got the new 4s however it has been about 1 month since Ive had this phone and not only is it back to its old ways but ios7 has if anything slowed it down even more to a point in which I no longer recieve phone calls at all, no missed call, no ringing, no notification, nothing. It has gotten to the point were Ive become so fed up with my iphone that i dont believe ill be staying with apple products anymore once i can upgrade. Hopefully some sort of help will come from all this.