I spoke with a rep on the phone and confirmed this. I also spoke with a rep over chat and got it in writing. My contract expires 9/30/10. Here is what the rep said (he also has a minor type-o):

4:29:04 PM EDT : Paul: Ok.
4:29:14 PM EDT : Paul: I have checked all information for you.
4:29:54 PM EDT : Paul: You van port in your services after August 30,2010 and there will not be any charges regarding ETF.

So, there it is, in writing, straight from Sprint. You can cancel anytime in the final month. The reason for this is because you actually pay for that month in advance, so once you enter that month of service, you have already paid the full 24 months you agreed to pay for. Do note that you won't get anything prorated back to you, though, for the part of the final month you don't use.