Tello started out as a Yelp for customer service. Founder and CEO Joe Beninato, a serial entrepreneur, had launched the ratings application in 2011 to evoke the spirit of the 1950′s, when the customer was still king.

But the business went in a different direction after creating PassTools, an API for building and managing boarding passes, tickets, and coupons in Apple’s Passbook for iOS 6.

Earlier this month, Beninato announced that he had sold Tello to the push messaging service Urban Airship.

Tello’s original mobile application gave customers a way to thank (or not) the individual employees who had helped them through the process of buying a car or booking a flight, which the companies could monitor.

In February, the company raised $2.7 million in a funding round led by True Ventures and Bullpen Capital to further grow the business.

“We had a lot of interest in Tello and Tello for Business over the two years but discovered that the sales cycles for selling to large businesses (retailers, banks, etc.) was incredibly long,” Beninato explained in an email.

“So this summer, when Apple announced Passbook would be part of iOS 6, we started thinking about what that would mean,” he said. “We spoke with our customers and discovered that we could really help in the pass creation process, and PassTools was born! We released PassTools on September 19th, the day that iOS 6 was released, and it took off. Thousands of businesses are now using PassTools to build and manage passes.”

Beninato was not the only one thinking about the possibilities for Passbook.

“When Scott Kveton, CEO of Urban Airship (who I had met previously) heard about our launch, he emailed me and we got together for coffee,” Beninato said. “Urban Airship is the global leader in high performance push messaging. Scott and I hit it off and decided that combining forces was the way to go.”

Beninato has joined Urban Airship as the general manager of its Digital Wallet team in Palo Alto, CA. “We’re a few weeks in,” he said, “and so far, so good!”