1. Log into My Ooma
2. Select Preferences --> Phone Numbers
2. Click the phone number you want to have access to
A pop-up will come up, showing you the phone number along with code to dial in order to gain access to the backup line.
Depending on what you selected during activation will determine how your landline is used.
If you selected to use your existing phone number with Ooma during activation, then you are required to plug a phone cord to the WALL port of the Ooma Hub or Telo that will provide dialtone from your existing phone service (can be a wall jack or other VoIP adapter).
In this case, all incoming calls to your landline number and outgoing local calls will utilize your landline service and all outgoing long distance calls will utilize your Ooma service.
If you selected a new Ooma provided number (or after your number is ported) and you have an Ooma Hub, you can plug the landline service into the WALL port of the Ooma Hub and if your power or internet connection to the Hub fails, after about 30 seconds, the phone service will switch over to the landline. You can do the same with the Telo, but only if internet connection to the Telo fails and not power will it switch over.