Braintree helps online businesses process credit card payments by providing a merchant account, payment gateway, recurring billing and credit card storage.

In 2007, Bryan Johnson was sick of working for a big corporation. He says, “I concluded that I’d rather live poor and hungry than work in a large, bureaucratic and political environment where I personally couldn’t see how my efforts created value.”

He started figuring out what it would take to do his own thing. “I figured that I needed to make at least $2,100 a month to leave,” he explains. “My wife and I had learned to live quite frugally. I had started a few other businesses before, so this uncertainty and financial risk was something I was accustomed to. I had a single objective: Get back into the saddle. I was going to do whatever it took to get there.“

He took a few days off work and flew out to Utah, where his old customers resided. He asked them if they’d switch their processing to his new company, Braintree. Quite a few of them did, collectively generating $6,200 a month. Braintree was officially up and running.

In 2010, Braintree generated $4.5MM in revenue, grew from 15 to 24 employees (now over 30), and doubled its customer base, according to Johnson. It powers payments for companies like LivingSocial, Github, OpenTable, and Animoto. And 99% of its customers come through word-of-mouth. “We’re on track to do $8 or $9 million in revenue during 2011,” Johnson says. “We also expect to rank among the top 50 on this year’s Inc. 500 list.“

According to Bryan Johnson:

“Bootstrapping a business requires a different mentality. It’s taught us to be frugal, hire slowly, and exercise caution as we grew the business. While companies that take funding can do those things, people have a tendency to behave differently when it’s not their money on the line.”

Check out full interview at 37signals