I looked through the Fannie Mae Servicing Guidelines, and in Section 604.02  (pg 153 of pdf labled as page 706-21 on document) it says:

"Sometimes a borrower may be reluctant to list his or her property for an amount that is less than that required to satisfy the entire debt unless the servicer provides written assurance that the short payoff will be accepted. When this happens, the servicer must request Fannie Mae’s prior approval of the preforeclosure sale before the property is listed. If Fannie Mae approves the sale (subject to receipt of a specific price), the servicer can add the requested assurance as an addendum to the listing agreement.
The servicer must explain to the borrower that he or she is expected to execute all of the documents that are necessary to sell the property—listing agreement, purchase/sales contract, closing documents, etc.—even though the documents will indicate that the sales proceeds must be paid to the mortgage holder. The servicer also must advise the borrower that he or she will remain responsible for maintenance of the property until it is sold and the settlement has occurred." (emphasis mine)

Now, I've been doing short sales for long enough to know that even when servicers "have to" do something, it doesn't mean that they always do it. Has anyone gotten short sales pre-approved by Fannie Mae before listing the property??? If so how difficullt and how long did it take?