If you call them and tell them that you want to check and see if the phones ESN is clean or not, they will tell you even if you're not a customer with them. I don't see what the issue is...?
Call (800) 922 0204, enter your phone number if you have one, also enter your PIN if it asks for one. On the main menu, press 0. If it asks if you want to take a survey, press 2. You might get a message that they're closed at this point. Press 3 and you might get asked about the survey again. Press 2 again, and you'll be connected, even if they're closed, and the rep will help with whatever.