I warn you ahead of time . . .
. . . this is going to sound like one of those Kip questions.
Is requiring college students to buy a Sprint cellphone with GPS tracking a legitimate government* function?
What if the student's dad works for AT&T? What if the student is Amish?
When I went to [S]MSU, they had an exclusive Coke contract so that no Pepsi vending machines would be allowed on campus, but even THEY did not require you to purchase Coke. You could always go to Dillon's or Git-n-Go and buy Pepsi and bring it back to campus.
[H/T 2 Two Johns No Waiting on KMOX.]
* - Montclair State is a public college, supported with tax dollars and therefore a tentacle of the government.