They're considered cheap.  Business cards, in terms of "real estate" for marketing materials and tools, are perhaps the least expensive way of getting your marketing message out to prospects.

Because they're so small, many small-business owners overlook the opportunities that exist with them to position your services in the mind of potential buyers.  Using the space well (design, content and graphics) as well as how you distribute them are all key elements on making the best of cheap business cards as a marketing tool.

Here are a few articles on how to use the calling card for your service: