[snom380]

I'm usually hesitant to give advice since I'm never in someone elses shoes, but here's some thoughts:

A lot of community building comes down to trust, whether you are developing a commercial or open source platform. As a customer and integrator/consultant/developer, I want to know that the platform is going to be around and supported. The bigger my company the higher the risk is.

Open sourcing your software sends signals to your customers and partners. Some will see it as a last ditch effort to make it successful, with the flip side being that if it doesn't happen, you're won't be maintaining it anymore. Will that make them more or less likely to use your software/help build your community?

So in your messaging you should be very clear in what you want to achieve, and how you plan to build a successful business around an open source or open core model, and how the others companies fit into this. How will you respond if another company takes your code and does the exact same thing you're trying to monetize, only better? Etc.

You should also be careful about positive feedback. Most people like to be nice and supportive, and won't say negative things. The only way to know whether you'll have success there is to see actual commitment (in money or work spent) with your product.

Finally as others have said, you shouldn't expect automatic success/community by open sourcing the code. You might end up attracting the sort of customers / developers that have the least incentive to contribute or pay for additional services, unless you go find those yourself.