It's called a project manager. One of the tasks of a PM is to make sure that the devs have time to do their work and manage any incoming information before relaying it to them.
Is this an emergency? Interrupt them.
Is this a minor inconvenience? Could this be talked about in the daily tomorrow morning? Is it something that someone else should actually know about? Block the information from the devs and deal with it in the chosen way.
Sometimes PMs don't do that and don't chastise the dev for not getting work done because they understand they're being interrupted. Then the dev is in a poor position where they want to do focused work but can't.
An assistant/secretary is what a project manager is supposed to be. The title is wrong in that it makes everybody think they are supposed to be a manager, a source of many problems in our line of work.
Edit: to answer your question about affording one, it seems around 5 developers can share one secretary, and split the cost. Incidentally, this is a usual setup with a PM as well, but again, they often seem to think their job is to manage the developers, not the project (which they also often don't do).
Is this an emergency? Interrupt them. Is this a minor inconvenience? Could this be talked about in the daily tomorrow morning? Is it something that someone else should actually know about? Block the information from the devs and deal with it in the chosen way.