Visible has not set a date yet. Last fall when they switched over to the new system they mentioned the old system would be shut down within a year. So sometime before beginning of September if they stay true to what they said last year.
Because it makes economic sense, not to run a infrastructure that they are planning to shut down.
If you dont want to risk losing your number, you can upgrade/ port to a different carrier while you can. Otherwise I have no idea with the blackbox with visible. This is the truth.