Microsoft promotes the soon-to-be-released Surface RT by saying it can let you:
Work anywhere, anytime with Windows RT and Office 2013 RT
And, yet, on the same page it states this, it also says:
Office Home & Student 2013 RT Preview and the final version are not for use in commercial, nonprofit, or revenue generating activities. Commercial license options available (sold separately).
AllAboutMicrosoft’s Mary Jo Foley explains the commercial license options:
Microsoft Office for Windows RT: How to move to a commercial-use license
However, you cannot use Office RT on a Surface RT for work related purposes out of the box without violating the Office RT license.