If you want to look at your itinerary to verify that your frequent flyer number is in the record, I agree that you have to call.

If you want to look at the itinerary for any other reason (e.g. to make sure the flight schedule has not changed, seat assignments), Delta has a feature on their website to check itineraries... you need the confirmation number (record locator) and the name in the reservation. You can do this whether the record contains a frequent flyer number or not. Just go to "itineraries" on the navigation bar on delta.com.