Ending monthly balance - as long as it is 0 by statement close date, no charge. but if there is any balance, there is a charge. one of our cards has a 3.16 balance I forgot it was there (charged to activate 1000 bonus miles for the payment protector), the charge was 0.03.

when you call to cancel, just be polite but firm, to tell the CSR upfront, no matter what he/she wants to say, is not going to change anything - so let's not waste his/her and your time, just to cancel it. You can cancel it ANY TIME even if you do not cancel it within the first 30 days "free" period. The UA card payment protector 1000 miles did not kick in the first month after enrollment, so needed to charge a small amount to generate a statement for the bonus to kick in.