Jun 12, 2013 · 3 minutes

Truecaller founders Nami Zarringhalam and Alan Mamedi

Stockholm, Sweden is home to a wealth of exciting startups and tech companies that are known as much for their sexy design and businesses as they are for their innovation, whether it be Spotify (music), Klarna (payments), Tictail (ecommerce), or King (games). One of the city's best-kept startup secrets, however, is a small company called Truecaller, whose business is about as prosaic as it is unsexy.

Founded in 2009, Truecaller has taken the old-school phonebook and turned it into a global crowdsourced directory. In the space of four years, that directory is now just a whisker away from hitting 1 billion listed numbers, and the company has just hit 20 million users. Just over a year ago, it had only 2 million users.

Truecaller's mobile app and website let you search for people anywhere in the world by name or phone number. Because it recognizes your social network, it has a pretty good idea of who you might be looking for even if you don't know the person's last name. You can maintain a social profile on the network associated with your phone number, and you can get recommendations for people to connect with via the Truecaller network. Once you're using Truecaller, you'll also see who's trying to call you, and you can set up a "block" list to filter out spammers.

screenshot_appleiphoneThe way Truecaller gathers its numbers might be uncomfortable for some. Essentially, it asks its members to share the contents of their phonebooks. That means your number might be in the directory without you even knowing it. Through a reverse lookup on the site, for instance, I found that my number was listed, as was my boss Sarah Lacy's.

Truecaller's service might not seem very appealing to Americans, who don't tend to make many random phone calls to people outside of their real-life networks, but it is going gangbusters in Asia and the Middle East. Almost a quarter of Truecaller's users are in the Middle East, where many men use the service to call women in the hope of finding a match. It's also popular in India, as evidenced by an article in The Hindu newspaper, in which three celebrities said the app is indispensable, because it lets them know if a call is worth picking up.

Today, Truecaller has published a document outlining the marketing methods that helped it reach such scale on a shoestring budget. The startup executed a five-point plan that helped it grow its Facebook "likes" and shares rapidly and massively, while also improving its reviews in app stores. The key moves were:

  1. Only display a "like" button when a user searches and successfully finds a result.
  2. Only ask a user to review the app once he has conducted five successful searches, or the first time the user marks a number as spam.
  3. After 30 days of non-use, send a push notification that highlights Truecaller's best features, such as call filtering.
  4. Let users send invitations to their friends via SMS, email, or Facebook.
  5. Use Facebook's news ticker to show when someone has searched for a number (but not which number they're looking for).
Those tactics seem straightforward, but the results were dramatic. As a result, Truecaller increased its monthly Facebook "likes" by 120 percent, increased the number of monthly shares by 2,000 percent over three months, and hit a Google Play rating of 4.3 stars from more than 100,000 reviews. In total, the company has more than 520,000 "likes" on Facebook.

Truecaller's business model relies in part on a limited-access API that it opened last month. Companies might find it useful for validating identities. Airlines, for instance, could use it to improve their customer support by getting access to the names of phone-number owners, while also being able to identify how they fit into the customer support network based on a Truecaller score.

The startup has raised $1.3 million in Series A funding from Open Ocean, a venture capital fund started by MySQL founder Michael Widenius, a strong supporter of Nordic startups.