Scheduling with Google messages. What does the roll-out information mean?
It means that feature will be enable by Google's server. You might already have the feature but you won't see it on the app's interface.

Surely they're not talking about something that requires cooperation from every ISP!?

It is not related to ISPs. Often due to the high number of users, some features are not &quot;open&quot; for all of them, but enable to users from the server (in this case Google's) slowly based on country, language, phone model, etc until all can use it.