You can use the TI-84, that was my deciding factor in buying it. I wanted him to be familiar with it and be able to develop programs in it to help his speed on the test.
My school allows phones to be used during passing periods, however we DO NOT allow them to be used as a calculator during tests. Kids will cheat if they really have a desire, but we can at least try to deter it as much as we can. So, becareful assuming you can just buy an app.....
