STOP!! Whatever you do don't skip a payment. You hold far more cards if you can prove hardship to the bank without being late. You need to get the help of a good real estate agent who specializes in helping people work on short sales. It is a specialized skill and shouldn't be done by just any agent.
The bank wants to see that you have lost your ability to pay the mortgage and more than anything they want to see that you aren't trying to take money away from them needlessly. First things first you want to list the home for a break even price and your agent will need to keep very good records of everything they have done to obtain the break even price. It isn't a fast process but you will then need to increment the price down until you get an offer. Once the offer is received your agent will need to submit it to the bank along with their marketing report. I hope that helps.
Please don't hesitate to contact me if you have any further questions.
The bank is not laughing at you. If you have asked the bank if they will accept a short sale, and they have said yes, they should ask you to fill out a financial packet which verifies your income, assets, and liabilities. Getting this to the bank asap will speed up the acceptance process once you have a purchase agreement. Skipping a payment is not the answer...you will do more harm then good, in my opinion.
I know someone in the short sale situation. She has been in contact with the bank constantly and given them a time frame when she will no longer be able to make payments. They have so far been very understanding and are willing to work with her and keep the home out of foreclosure. The banks know how desperate people are because they have so many people in your situation. So far your credit has not been hurt by the situation, missing a payment could put a dent in that, as well as your relationship with the bank.