You might remember David Glickman. In 1998, Glickman's Justice Technology, which offered a super-cheap way to make inter­national calls on landlines, topped the Inc. 500. More than 15 years later, Glickman, 49, has another telco, Costa Mesa, California-based Ultra Mobile, which has snagged the same spot doing a similar thing, but this time for SIM card-enabled mobile phones.

--As told to Lindsay Blakely

I always felt it an injustice that phone companies allow you to call locally for next to nothing, but when you make an international call, they jack up the price ridiculously high. Fifteen years later, mobile companies are doing the same thing. And I'm still definitely a David who has no love lost for Goliath.

After Justice, my partners and I started other telecom ventures. One was Hometown Telecom, whose flagship product was India­LD. It worked much like a calling card. Folks calling from the U.S. to India dialed a special access number and punched in a code, and we gave them the best rates. It was so successful that the two largest Indian carriers exited the market. But we weren't doing huge numbers, and this was not the most seamless way to make international calls.

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So we thought, why can't a carrier offer calling-card rates or even free global calls and roll up everything together in a mobile plan with texting and data? No access numbers. No PINs. So we became a mobile virtual network operator [MVNO] that focuses specifically on the 46 million people living in America who weren't born here.

We thought with our experience, it would be easy to build a large customer base using affiliate internet marketing and Google AdWords--strategies that've always worked for us. With IndiaLD, we paid $30 to $50 to acquire each customer, but they usually referred three more, so it was really more like $10 to $15. When we launched Ultra, acquiring a customer cost more like $250--customers didn't want to change mobile carriers after seeing just an internet ad.

So we went to CTIA Super Mobility, one of the biggest annual wireless conventions, and pitched as many independent wireless stores and distributors as we could. It paid off--a few months after launch, we were in about 3,000 stores; now we're in about 25,000 nationwide. We hired a team experienced with growing an MVNO brand. We came up with one of the most competitive plans on the market for international talk, text, and data.

Our frenetic pace requires a very specific kind of person, which is why we're more than 80 percent Millennials. When we're hiring, we don't interview them; they interview us. We give them a lot of those Silicon Valley perks, things like midday yoga, free food, dogs in the office. But we also give them a higher purpose: We're removing barriers to communication, and that's what gets us up in the morning.