We’ve long known that calls are much more valuable than clicks to small businesses in particular, but also to many larger entities with call-center sales operations. However… it’s taken PPCall much longer to get going than I originally anticipated.

Sterling sees pay-per-call growth in traditional media and mobile. He also notes that pay-per-call programs are now increasingly being used in print Yellow Page directories such as AT&T which just announced pay-per-call programs via the YPmobile App for iPhone and iTouch . Merchant Circle also recently announced pay-per-acquisition pricing – including pay-per-call.

And it’s not just AT&T and Merchant Circle. Other traditional yellow page publishes are renewing interest, and venture rounds by MojoPages, Balihoo, RingRevenue, as well as the TechCrunch50 launch of Redbeacon and Yext show that there is a growing supply of pay per call offerings coming into the mobile local search market.

In fact, I just read a blog post lamenting the poor service delivered to a pay-per-call advertiser. The merchant—who was irate that he received wrong number calls and was charged inappropriately—reminded me of what can go wrong with an advertiser’s pay-per-call campaign.

All of this brings home a point: as more and more search engine marketers, publishers and others in the mobile local search ecosystem are discovering, pay-per-call is not as easy as it appears on the surface. If your local business is being pitched by a provider who just provisions a few tracking numbers, begins charging for calls and then expects to roll in the dough, you need to be prepared to ask a few hard questions.

Five rules for every local merchant interested in pay-per-call pricing

Make a good first impression. If the first calls received from your campaign are wrong numbers look out. Despite best intentions, assigned numbers (necessary of course for pay-per-call), are never entirely clean. Before a number is assigned, your provider should be monitoring for wrong number calls.

Be selective. Pay-per-call can succeed for local advertisers focused on phone lead generation, but it may not be right for your business. Your business should not rely on walk-in traffic (retail); the cost of sale cannot be too low, or too high; and sales generally need to be closed every few calls (high sales to call ratio). You are an ideal pay-per-call advertising candidate if you have advertised in the yellow pages, newspapers, FSIs, Valpak or other mailers, radio or local TV. Business-to-business (B2B) advertisers or niche merchants are not typically good candidates for pay-per-call.

Be prepared to serve your callers. I founded my company on the premise that pay-per-call must benefit the consumer, merchant and publisher. Ten dollars per call may be a great deal for you, but your business needs to be properly staffed and trained to answer the phone. Without a connection to your helpful, available staff, the consumer is not served. If your business does not have the infrastructure to serve clients by phone, pay-per-call may not be for you.

Be able to close a sale or make an appointment by phone. I had a client—a direct mail publisher—whose advertiser complained that they did not make any sales as a result of the pay-per-call leads. We were recording the calls (with permission) for the client and discovered that the leads from the publisher were good, but the advertiser’s staff couldn’t sell.

Calls prove return on advertising investment (ROI) even without pay-per-call pricing. If pay-per-call isn’t right for your business, don’t give up on the numerous benefits of tracking and routing calls.

Look for innovators and leaders when comparing pay-per-call offerings. Yext demonstrated an example of this innovative thinking at TechCrunch50. Leakage and dirty calls are a real problem with pay-per-call. Yext is using analytics to examine key words for relevance and filter out junk calls.

The TechCruch50 winner, Redbeacon—while not focused on pay per call, or calls at all—is trying to solve the problem of merchant availability. This is closely related to pay-per-call (see Rule #3). If your staff is not available to respond to a call, the consumer is not served. The merchant who answers the phone is generally more available than the merchant that does not—especially over a series of calls.

Successful implementation of pay-per-call requires bottom up thinking with the same new product development rigor as any major new advertising or lead generation product. The next generation of Pay-per-call 2.0 insures a high level of satisfaction with the quality of your callers (consumers) by including detailed analytics and reporting to identify repeat calls by caller ID and other calling patterns; category management to deliver the best leads to the right merchants; pricing models that optimize value; and finally advanced, real-time call routing applications to deal wrong numbers, vendors and other unwanted calls.

Despite several years of building expectation, pay-per-call is still a relatively new pricing model within mobile local search. Providers entering this market must be prepared for a fairly steep learning curve and merchants need to be prepared to ask the right questions.