Greetings:
Just a heads-up: Google has now migrated their new Google Voice signup flow to the new Google Voice user interface (the old, "Legacy" UI will no longer work for new signup).
As part of this change, all new configurations will be required to sign up with a Google-supplied Google Voice phone number, before (optionally) porting in a number. The option to port in a number instead is no longer presented. If you want to port in a number, you'll need to first complete the setup process with a GV-supplied number, and then follow the port process. If you wish, you can either keep the temporary GV number or delete it after the port.
See: https://support.google.com/voice/answer/1065667?hl=en&ref_topic=1708124