If you have a compelling value proposition, you can crisply articulate how you solve a specific problem, and you can accurately target prospective buyers who you know have that specific problem, then cold calling can work. Your "pitch" has to be short and immediately cut to the chase so that you get past the first urge to say "bye" or hit the delete button on voicemail. You must be prepared though for some "less than fun" rejections. Don't take it personally. Keep track of what worked and what didn't - keywords in the pitch, time of day you called, etc.
You may find it more effective to work with your existing client base and ask them for recommendations. You could offer them some form of incentive to help you. "Two months of free service for every new client you refer who signs a contract".
This should all be in the context of your broader marketing plan. What's your target market? what are the trigger events that make a prospect most likely to buy from you? What are the organizations that serve this market and how can you participate in these? What does your web site say that quickly tells a prospect how you solve their problem? How are you using Twitter and other social media to interact with your target prospects? Who are the industry analysts and press people who cover your industry and how can you reach them?
Key point - just as you do for other parts of your business - measure the time you're investing versus the return and see if it really is a good use of your time versus other approaches to growing your business.