You might want to consider a "department" strategy. Structure your service as something that an individual department of a larger company can get hold of witho

You might want to consider a "department" strategy. Structure your service as something that an individual department of a larger company can get hold of without support from IT, approval from on high, or a mess of purchase orders. 37Signals has talked about this in the past, a couple people within a big company start using Basecamp for some one off thing they're working on, then a few more people get added to the project so they get the departmental credit card (used for buying office supplies) and sign up. A few months down the line everyone in the group is using the service.