As far as I know, I have no credit history, besides maybe a few low cost items charged to a debit/credit card. Would that in itself make them require a deposit or should I make sure that there's not anything sketchy going on with my credit?

(my carrier is t mobile, if it makes any difference)

A deposit typically means either a lower score or not enough credit history. Get your free annual credit report and check it out. Don't worry too much about it though, deposits for services are becoming a lot more frequent. Good luck!

That is exactly why you have to put a deposit. You do not have established credit yet. Doesn't mean you have bad credit at all. Just means you have not built it up yet. Now, If you had a $500 deposit then you have some bad credit.