Ask HN: How to validate an idea that involves both users and businesses?

When you have an idea that is consumer oriented, there are several well-known ways in which you can validate it to see if people are interested before building the whole thing (e.g. put up a simple wordpress landing page, etc)

What happens when you have an idea for selling a service to companies but also requires lots of users to sign up to make it valuable to the companies you are selling to?

It seems like a chicken-and-egg problem. Users won't sign up unless many companies use this service and companies won't sign on unless many users sign up.

Are there any good strategies for attacking this problem, besides just talking to companies and gauging their interest if you had users, and having some incentives for early-adopters to sign up to beef up the population of users?