Agree with Bob. Loan servicing is the first step because you need to stay RESPA compliant with your activities, and it is relatively inexpensive. Generally when you purchase a note it is already boarded with a servicer, so you could either leave it there or have servicing transferred to your own servicer. If you transfer servicing, you will need to wait for the "goodbye" and "hello" letters to go out before attempting to contact the borrower.
There are a handful of states where you need a license for debt collection, but most are not that way. I contact (or attempt to contact) borrowers regularly as part of my workout strategy, but if I am working in a new state I check with the servicer since they know the state laws better than I do.
Regarding the loan modification question, you don't need a mortgage brokers license. You can change the terms of the loan within limits and your servicer should be able to do the loan mod on your behalf.