How do I get my cell phone to disconnect from the internet?

Hi! I have an LG Rumor phone but no internet plan. I connect to the internet sometimes to send picture mail, but I have no idea how to disconnect from it; short of turning my phone off for 4 hours, which is not the most convenient. Anybody know how ot disconnect so it doesn’t sit there charging me an extra 50 bucks extra for one day of use?!