Being one of these students, I know that even in high school they required one of these expensive calculators (specifically TI-83/84). I think you will find most of your students already posses those calculators and those that don't will eventually need one.
(even though the TI calculators are extremely overpriced, they are really the only way to go... about $100)
I could also see using a dictionary, but an iPod touch or iPhone?! if you've got wifi, they will be all over the internet, Any information they want, they can get... not really the point of the test is it?