After I bought my Pre I sold my old SERO plan to avoid paying the ETF. If you happen to do this, don't bother calling Sprint's Customer Service when it comes time to initiate the transfer. I called multiple times and was told each time that I could not transfer liability of a SERO plan. Reasons given: "it's an employee plan" or "it's a special plan", etc, etc.

Just make sure the person who is taking ownership of the plan is on standby and you have their name and contact #, then call 1-866-954-0492. When prompted, select Option #2. When they ask for a reference number; just give them the phone # on the plan you are transferring. This is the business unit within Sprint that handles changes of ownership exclusively -- they'll get the info they need from you; put you on hold, then will call the other person and get their info. Bip-bip, the whole process took ~5 min and the changes take effect on your account immediately!

Credit goes to the OP over on howardforums where I found the above info: HowardForums: Your Mobile Phone Community & Resource - Sero Transfer of Liability (TOL) question? Who to call?