Button problems

Hello everyone, I've had my iPhone 3G for almost a year now and never had any problems with it until recently. My main button will go to the main screen with the apps, but when I tap on an app, it will not let me go back to the main screen sometimes and I have to turn it off and on and even then sometimes it doesn't work. I recently added a Wi-Fi network, but it works fine most of the time. Throughout the day it can be fine, but then it just acts up and I have to keep restarting it and even when I put it on the charger, it still does it sometimes. Is it bad enough to get a new one?

Thanks!