I've installed speed camera and rest area announcements on my 1490T, with alerts based on distance. The 1490T is running v 4.70 software.
Periodically, and I am not certain what the trigger event is, the 1490T stops announcing navigation directions or alerts. The only way to get the voice prompts back is to turn the GPS off and back on again.
We've really gotten lost a couple of times because we were expecting voice announcements of turns and they never happened.