Some blackberry applications are able to set their title depending on how many messages are unread. Examples are the Gmail and ubertwitter app. Gmail will set the title to “GMail (20)” to indicate there are 20 unread message. This shows up when hovering over the icon on the main blackberry screen, or when viewing the running apps selector. Ubertwitter does the same.
I’ve looked through the blackberry API and done quite a bit of googling, but I don’t see any likely candidate for setting this string. The ApplicationDescriptor would be a good candidate type for this setting, but all the properties are read-only. There are no setters available, save for ‘PowerOnBehavior’
You should be able to use net.rim.blackberry.api.homescreen API.
In particular (Untested)