iPhone takes forever to turn on

Every night I have my iPhone charging. If I don't have it charging, I have it on my nightstand. When I wake up in the morning, I go to hit the sleep/wake up button on the top and it does not turn on. So I wait a few minutes later and it does not turn on. I have also had this problem at random times during the day. I have a 45 min drive to work everyday and I really like to use my iPod on the phone to listen to music. It does not turn on for a half hour. I have tried resetting the phone, I've even tried plugging it back into the charger and that does not work. I have missed phonecalls from work because of this problem. With only having 2 buttons, it shouldn't be that hard to get working. Has anyone else ever experienced this problem? Could my phone be defective? This is getting really aggrivating! I've already got past and accepted that I cannot receive normal MMS messages on the phone. My power issue I will not be able to get by. Plugging my phone into the computer and accessing it through iTunes is not an option for me in the mornings either.