Have you considered rolling back or sharply limiting your free trials? With the exception of people you've made commitments to, if they aren't accomplishing a business goal for you, you don't owe the world them. There is nothing intrinsic about SaaS that says there has to be a free plan. (Additional options: aggressively using the free plan as a viral spread mechanism. Your free competitors do this, as I learned the other day when on a sales call organized by somebody who would have happily dropped $50 to remove the external branding for that single phone call if they were aware of your option existing.)

We also run on Twilio, and have a 30 day free trial with CC required upfront. While we still have marginal expenses to service free trials in a way that many SaaSes do not, the costs are not terrible and easy to justify as a cost of customer acquisition. (We shoot for, and mostly get, 80%+ margins on the paid plans.)

If you're ever in the mood to chitchat about this, drop me an email. I'd be happy to share about how e.g. moving a bit upmarket and doing a bit of enterprise sales has worked for us.

Putting my marketing hat on, I'd strongly suggest Patio11's blog on inbound marketing. He's really good and the points he make are dead on (the big marketers are basically doing the same thing except paying Marketo and Hubspot for automation).

I think it would be difficult to do 5000 participants in a conf call on stock freeswitch boxes, but we've done over 20k using Kazoo (Which leverages FreeSWITCH as the media server). Our secret sauce is an abstraction layer and custom freeswitch modules for distributed scaling. When you get over a few hundred participants in a conference call you're always doing some sort of bridging between boxen and when you chain lots and lots of boxes together keeping state across the cluster becomes a challenge. We've done a lot of work handling distributed state in conferences; it was a pain.

If you want us to host something like that for you, drop me a line in my inbox. Contact info in my profile (we're also open-source if you wanna get your hands dirty).

Please note: Kazoo (our stack) is built for carrier deployments, and requires a minimum of 8 servers for full redundancy. You can get by with as few as two but full redundancy requires 8 (and is thus our recommended minimum configuration). But it does have all of the stuff you've mentioned and you don't need beefy hardware to do it either.