IM has already been in corporate America for a while. I've worked for a couple Fortune 200 companies over the last 10 years and all of them (plus the smaller companies) have all had IM. The services listed in the article I've never heard of, but it seems to overlook the already obvious big dogs that have been out there:
SameTime. This used to be used when the company was Lotus Notes based.
Microsoft Communicator. The IM program that is bundled with the enterprise Exchange and collab tools that Microsoft provides.
Skype. For companies that might have a looser network policy, or have to deal with talking to many external clients, this is the easiest way to communicate cheaply, and also has pretty high usage vs something like asking your customer to install and figure out how to use an IRC client.
This article is saying that most of messengers are only exposed to internal employees. When we want to communicate with customers or partners, we fall back to traditional methods like email or phone. If someone can figure out this external communication, this'll be a big market.
It's been this way for a while. Corporate IM that is integrated with ActiveDirectory and other backoffice apps (document repos, source control, continuous integration) is super useful. HipChat is our current champ. The only time it falls apart is when you want to chat with a customer/vendor/etc. Then you're back to phones. If someone can break down that 4th wall, they will be rich.
My highest usage of instant messaging came when I was working at a large consulting firm. Everyone used it there, because we were scattered, and phone messages and email were too slow. I don't think it's going corporate, I think it's been corporate.