There are many ways to milk a cloud. IBM (NYSE:IBM) is launching a cloud-based email service that could end up stealing sales from both Microsoft (NASDAQ:MSFT) and Google (NASDAQ:GOOG).

The IBM LotusLive iNotes service is a cloud computing email platform that's aimed squarely at corporate customers. For a $3 monthly fee per license, you can get a secure email application that's hosted by IBM and available from anywhere. For starters, IBM will provide the cloud hosting, but there may be an installable version later on; many IT directors simply prefer to host their own private clouds with full control over the environment. "It's fair to say we're pretty trusted," says Sean Poulley, IBM's vice president of cloud services.

iNotes takes systems management out of the equation and presents a simple, direct way to get and send mail from anywhere, including from smartphones like Research In Motion's (NASDAQ:RIMM) BlackBerry or Apple's (NASDAQ:AAPL) iPhone. And there are early signs that mobile mailing might be what IBM really is shooting for here.

IBM holds up Nokia (NYSE:NOK) as an early customer and partner. Today, 1.5 million Nokia phones come equipped with the IBM LotusLive messaging software, so it's an easy next step to sign up for an iNotes email address right from the phone without ever touching a computer. That sounds a bit like IBM will market this service directly to consumers on the street, but the real money is in the corporate market.

The obvious target market is businesses that use Google's Gmail and Apps services now. Google's platform costs $50 a year per user and IBM's solution comes out to $36 a year. Granted, Google Apps accounts also come with other bells and whistles like online word processing, and Google's 25 GB of storage is much roomier than IBM's 1 GB. But many small and medium businesses may prefer the no-frills approach, especially in these times of tight IT budgets.

This is also a direct attack on Microsoft's huge installed base of Exchange email servers. At $36 a year, iNotes comes a whole lot cheaper than a Microsoft platform that costs thousands to install and maintain. The same is true of Microsoft's Exchange Hosted Services, which provides a similar cloudy experience starting at $4.50/month per user, but includes additional layers of fees.

iNotes alone will hardly move IBM's big, blue needle very far, but the company is showing real commitment to the idea of cloud computing. IBM will challenge cloud-computing powerhouses like Google, Amazon.com (NASDAQ:AMZN), and Microsoft for years to come.

I'm using Gmail every day. Which Web mail platform would you trust with your business mail? Discuss in the comments below.

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Fool contributor Anders Bylund owns shares in Google, but he holds no other position in any of the companies discussed here. You can check out Anders' holdings and a concise bio if you like, and The Motley Fool is investors writing for investors.