As a digital interactive software development shop serving the agency marketplace here is what we do after many years of experimentation.
We hire recent college graduates (Masters Degree Level) in Kharkov where our development offices are. We look for people who have done internships in the U.S. We start them out on sales administration tasks, expose them to pitches, send them to basic web development school, teach them the organizational structure of our prospective clients, and invest time practicing, practicing, practicing with them.
Their goal is to qualify a suspect, and not be annoying. Above all we train them to be honest, and to be themselves.
Selling dev using a call center - or buying one of those marketing lists - is a waste of money. Development is not a commodity, it is a relationship based on trust that must be earned. I get five, six calls a week from call centers pushing development, I play along, 99.999% of them are so bad I feel sorry for them.
We didn't do any of this until I had sold to the end of my contacts, and my contacts friends. If you're just starting out you need to find your voice, identify your strong points, get a rock solid process, and build a good portfolio before you throw money at outbound marketing. Building a successful dev shop takes a couple of years of foundation building, and a lot of very hard work.
In the development business clients are not hard to find. It's the good clients that are tricky...