Bad ESN, iPhone 4S sprint says it's okay, replaced parts no sim.

So I recently sold my phone via eBay and when the new owner tried to activate it via the same carrier I had used it with (sprint) they told him it had a bad ESN. Now I sold it to him without the SIM card and with a new replacement screen already installed (previous/original had shattered into a million pieces).

So I called sprint(I'm still with them), and they looked up the phone and told me the ESN was good and ready for activation.

Would replacing the front screen have changed the ESN or would not having the SIM card invalidate the ESN?

Sprint iPhone 4S 32gb. Everything on iPhone is original with exception to the front screen.

Phone is being returned to me so I hope to resolve it otherwise Ill just put it on clear talk and use it myself.