what happens to arrears in a loan modification

Hi,

I have just started my marketing efforts here in Southern California, and I'm targeting homeowners who have received a notice of default or notice of sale. When I approach these homeowners, most of them say they are currently applying for a loan modification. Some of these people haven't paid their loans for months and owe upwards of 30,000 to 40,000 in arrears. I was wondering what happens to the arrears if they qualify for a loan modification? Do they still have to pay the balance to reinstate their loan? Does the balance get absorbed into the modification? Any information relating to this would be much appreciated. Thank you