You are not a citizen until you are sworn in. If you are denied because of failure to pass the English or the civics test, you will be automatically rescheduled within 90 days. If you are not approved for some other reason, you may be given time to overcome the problem.
For 2009, the American Opportunity Credit--which is a variation of the Hope Credit--will be allowed for 4 years. For years before and after the new credit is allowed, the Hope credit is supposed to be for 2 years.
That does sound odd! It will depend on what prepaid plan you're using as to how long the credit will last. For example the old $2 a day 4G ready prepaid plan, if only $10 is applied the credit will expire after 10 days that being said the service shouldn't expire at this point in time.