Leading product at Twitter and accepting investments at Square? Business seems a breeze for Jack Dorsey.

The serial entrepreneur’s newest startup, electronic payments service Square, announced Wednesday that it has received an unspecified investment from Visa. As part of the deal, an unnamed Visa executive now sits on Square’s advisory board.

The two-year-old company this past January raised a $27.5 million Series B round led by Sequoia Capital at a $240 million valuation. Khosla Ventures led Square’s $10 million Series A in 2009, which valued the startup at $45 million.

For the uninitiated, Square makes a little white accessory for iPhone, iPad and Android and gives it out to businesses for free. After downloading the free Square app, those businesses can start accepting credit card payments (Visa, Mastercard, American Express and Discover) right from their mobile device, wherever they might be. Individuals can also purchase the Square card reader from the Apple Store for just $10.

Square takes 2.75 percent from every transaction. A couple months ago, the company said it was processing one million payments per day. I’ve reached out to the company to see if payments are still running in that range. There’s no telling what the average transaction sale is, but even at the most comfortably low estimate, Square should still be taking in tens of millions of dollars each month.

Investing in Square is a smart move, Visa believes, exactly because it sees and understands that mobile devices are fundamentally altering the way payments are done. Not only that, but Square is opening up the world of credit card payments to tons of smaller merchants that previously couldn’t afford the time or money involved in setting up their point-of-sale to accept credit.

After tweeting the Visa investment news, Dorsey went on to say that Square now employs 117 people--and they’re still looking for new hires. Half of the 20 or so open positions are for software engineers in a wide range of specialties, along with a few others in accounting, design, human resources, operations and research.

(By the way, if you’re looking for a laugh, click through to some of those job postings. Somebody at Square--Jack?--either has a huge sense of humor or else just a serious affinity to style sense. Software engineers at Square are required to “exhibit a bevy of complex and well-wrought hair styles,” copywriters must have a “good haircut” and preferred business recruiters will have “cool shoes” and “good jokes.”)