I am familiar with Sun Trust and from their website it is clear that they are trying to assist borrowers who are 60 days late first. This does not mean to go late to get their attention however. However, since he is now late on his mortgage you might look for a range of options available at this point. There is the FHA write down refinance. There is a short sale, there is a Deed in Lieu option. There are several options. Here is a good website that will go over all your options. Good luck!
I am not familiar with Sun Trust, but I know all of the banks are willing to make some type of adjustment, the owner just needs to have a hardship. My advice would be for you to speak with the bank and see what arrangement you can make.
While I'm not aware of SunTrust's particular policies, I'm sure if your father can show hardship in making his payments that the lender will listen and perhaps be able to modify his loan for a short/long period. It is always a possibility and certainly worth asking. The bank is more likely to deal with someone who can make the lower payments if they choose to modify the loan than someone who can't make the payments at all. Keep in mind, it takes about 3 months of non-payment before the mortgage goes into default, and if you talk to the bank early it looks better and they will be more likely to work with you.
Let me know if you need any further help and good luck!
Keller Williams Realty