I work for a 75-staff company on a pretty tight budget, and we have office 365. For us to use slack with SSO and have more than 10k messages, we'd have to pay

I work for a 75-staff company on a pretty tight budget, and we have office 365. For us to use slack with SSO and have more than 10k messages, we'd have to pay about $11k/yr. Teams, we're already paying for with o365 (and even if we weren't on o365 yet, E1 plan is approx $7k/yr and includes teams, exchange... sharepoint (not that I'd use that)). That's what's going to prevent Lync/s4b from going down the drain.