Indymac is controlled by the FDIC and are following the FDIC modication model. You must contact them and ask for the modification application. You must be honest and provide income documentation (among other things). You must be able to qualify for the modification. If you cannot document income or don't make enough money to qualify for a modified payment, you will not be eligible.
I have a friend who is under contract modifying loans for FDIC seized banks. They generally have been doing a stepped up modification starting @ 3% that increases .5% for the next five years. After year five, the rate is fixed @ market. This was as of 2 months ago so it has likely changed since then.
4 months behind means that a notice of default will be filed. By month 6 you will be up for auction. Time is of the essence and you must grab the bull by the horns and contact Indymac.