You put a piece of bread on either side of the iphone. Then you wrap it up in aluminum foil so it looks like it's your lunch. Then you just say that it is your lunch.
or
You wear a really big belt buckle and put your iphone 4 behind that.
or
give your iphone 4 a make over and take all the metal components out, however, you'll have to do it right or you wont be able to use your iphone anymore.
or
you buy lots of these: http://www.thinkgeek.com/geektoys/cubegoodies/bbe8/ , then you take them and cover them up and make it in the shape of a large rectangular prism. Then make up some lame excuse on how you are doing this for a school project something like magnetic strength compared to shape and size.
or
you bribe the security crew
or
you buy this: http://www.metaldetectingsecrets.com/
or
look at some links that will help you:
http://www.schneier.com/blog/archives/2004/10/foiling_metal_d.html
(shove it down your pants and into your "area", when security demands to inspect "it", call it harassment)
http://www.wikihowl.com/get-your-phone-into-school.html (really good idea)
or
vote me as best answer...i tried