To my knowledge, so far there is no application that ships with the CallManager to provide this functionality. The closest solution to this would be using the idle url as described below.
You can write your own application to push text to a phone. This text can be cleared by the user by pressing the exit softkey, or else you can set the refresh header to have it automatically time out and return to the idle url or some other application, etc. This is cleared automatically when the user picks up the handset. It is not cleared automatically when a call comes in, so caller id is blocked while the application is running (the same applies to the idle url below). Check out the "IP Phone Services for Developers" forum for more information on this, as there are a few threads covering this.
Alternatively, you could set up your phones using an "idle url" (an idle url is simply a Cisco XML service that runs automatically when the phone is idle). Then set that web pages refresh heading to refresh every so often, and the "content" of the idle url should be current enough to use to send general messages etc. Each dept could have their own idle url, or even each specific user, though this adds a bit of administration overhead as you have to assign idle urls to each user I believe (unless you decide to use one idle url for all users, in which case you assign the idle url globally). Still, it might be an option.
Or you could use a premade application such as Berbee's. There are a number of options available, it just depends on which option suits your needs.
