To transfer, email support@voipo.com and explain you want to do LNP (Line Number Portability) for xxx-xxx-xxxx to add as a Virtual number. They will likely send you a form to be filled out and faxed.

I cannot recall if there is simply a web interface for it?
They have become very efficient at the follow-through and completion.
Don't cancel the old service until the transfer is complete and working!