my iphone 3g is getting very slow when I try to access the contact or any apps on the phone. It is not jailbroken. Is there a way to speed it up to what it use to.
Did you try simply turning the phone off and on. Not just sleeping it, but actually turning it off and then back on (you will see the Apple logo on the screen for a bit while it reboots).
I would try this before the restore, it is quicker and easier...
You could try a reboot (press home and power buttons until the phone turns off), or you could try a RESET ALL SETTINGS (not erase all content and data). Otherwise, do a restore.