You aren't making much sense with your terminology.
"Porting" means transferring control of a phone number from one telephone carrier to another one. Service on the losing carrier is canceled, and service on the gaining carrier starts.
You can't port landlines directly to Google Voice. What did you do, exactly? For example, did you have a landline phone number with service on a landline carrier, and then you ported that number to a mobile carrier, and finally, you ported that number to Google Voice? If not, explain what you did, in detail.
If so, then you now have two Google Voice phone numbers (not a "landline" and a "Google Voice number").
If that's the case, then, if you want to keep the original Google Voice number, you need to pay another $20 fee to make it permanent. Once you do that, you can make outbound calls using the caller ID of either Google Voice number, by selecting which number is "Primary" and the other one will be "Secondary". Outbound calls will show the caller ID of the Primary number, and you can swap primary/secondary roles for free, at any time.
Inbound calls to either Google Voice number will ring the same OBiTALK line and the same mobile number or smartphone app clients.