There are a couple of key issues of which you should be aware.
The one thing going in your favor is that the lenders are more inclined to work with you because of financial climate. The bad news is the economy has definitely shifted downward so time is of the essence.
You basically have to different options that both require a Realtor experienced in short sales to help you analyze your situation.
Option #1 is try to re-negotiate the terms of your loan. Called a Loan Modification, it is possible that you will be able to have the lender re-structure your loan so the payments are affordable. In this scenario you will need to qualify for the loan, so part of this process is explaining why at one time you did qualify for the loans your currently have, and how it is that now you are no longer qualified.
Option #2 is to explain to the lender that due to circumstances beyond your control you are no longer able to the mortgage payments and that it is a situation which is not going to reverse itself. The best thing for the lenders (both first and second) to do is to allow you to sell your home at a loss.
The challenge here is that the two options require different tactics. if you try to qualify for a loan modification, and the lenders reject it, then try to qualify for a short sale, they may look at the application data for the loan modification and say "hey, you should qualify to keep paying your existing mortgage".
I would be happy to refer you to an expert in your area that can analyze your situation and give you your alternatives, and the pros and cons of each.
Note that there are many people who have experienced a decline in value, so just because your home's value has declined is not a valid reason for a lender to work with you. Also, there are people that have experienced real hardships, including medical bills, death, divorce, job loss, that really need and deserve a loan modification or a short sale.
The benefit to you speaking with a local expert is you can then get the facts you need to make the right decision.