I have no idea how many credit card reading cell phone accessories exist on the market today; I only know one by name… Square.

That’s probably why, according to TechCrunch, Square just closed a $200M round of funding that left the company valued at $3.25B.

That’s the official retail price for the Mergers & Acquisitions people. Much like Instagram’s $1B price tag, it’s a purely conceptual figure for most of us, based on a bunch of projections that are slightly more scientific that a fantasy football draft (see Facebook’s IPO disaster).

Still, the list of investors includes names like Citi Ventures and Starbucks, which is clearly bullish on mobile payment technology.

Square’s primary product is the iOS and Android compatible attachment (I’m not a big fan of the term “dongle”), which has proven to be one of the most practical ways to bridge the digital payment gap in an increasingly cashless society.

Not only do I know people who’ve been processing payments on the square for the better part of a year, we have one in the office, in case we ever actually have occasion to use it.

Honestly, the 2.75% hit is negligible when compared to the increase in sales you can make to people whose wallets are full of plastic. A few weeks ago, I manned the merch booth at a friend’s concert. I bet we sold twice as many t-shirts and CDs because we were armed with a square… it was a powerful and practical case study for how useful this technology can be.

If you’ve ever sold your wares at a craft fair or you’ve been in a band, then you know how many sales you lose when you point someone toward an ATM machine and they never return.