Ummm.... isn't this what this migration is all about? so VF doesn't have to pay Spark for a pots service when it can generate one perfectly well via voip from it's own kit?
It makes good business sense apart from the missed opportunity to give away free feature services like CLI and so on.
Especially when as their link so proudly says, "There will be no change to the amount you're charged for your Broadband and phone service." - so getting a worse service for the same price is hardly an upgrade.