my iphone 4 is runny very slow. it wont recieve messages quickly and it wont send them quickly either. it takes so long to send and receive messages. what do i do?

Try This...

Close All Open Apps... Sign Out of your Account... Perform a Reset... Try again...

Reset ( No Data will be Lost )

Press and hold the Sleep/Wake button and the Home button at the same time for at least ten seconds, until the Apple logo appears. Release the Buttons.

http://support.apple.com/kb/ht1430

Also consider Deleting any Apps you have Purchased / Downloaded but you now never use..