ESN Swap and Unlocking

[Gusy]

My situation is this one, I bough the HTC TP in ebay with a clean ESN, the person who sold it say in the description that it was for sprint, I'm Pretty sure that the phone can be unlocked and flashed. In he's description he said something about doing the ESN swap when I received the phone, but my question is:

Should I unlock and flash the phone before doing the ESN Swap( or never do the ESN Swap) or should I do the ESN Swap and then do the Unlock and Flashing?

-Thanks in advance