usna15: Are you applying for class of 2014? Were you accepted to NASS for this year? Your screen name makes it seem as though you would be going for 2015.
If you're currently a HS junior (USNA Class of 2014), you should receive a letter from USNA with your candidate number close to the same time you receive(d) notification regarding your application to NASS. If you did not apply to NASS, your letter should arrive ~6-8 weeks after you fill out the USNA preliminary application. You will only receive a candidate number if the info on your NASS/preliminary application shows that you are in the range of grades/test scores that woulld be competitive for getting an appointment.
If you are a HS sophomore (Class of 2015 applicant), you cannot apply until next year's NASS application comes on line. If USNA does it the same way as in the past few years, the NASS application should be available 1 February 2010.
The short answer to your question: if you are applying for 2014 and you applied for NASS OR submitted your preliminary application more than 8 weeks ago, then a call to the USNA CGO about getting a candidate number would not (IMO) be out of line.