What are the "both numbers" to which you refer?
What is plugged into the Telo?
Connect a phone to your Ooma to use your Ooma number; connect a separate phone to your walljack to use your AT&T landline number.
If you can forward your AT&T number to your Ooma number, great! Then you can do that and then just use the phone connected to your Ooma. Your outgoing calleird will show your Ooma number before you port your AT&T number to Ooma though.
To order number port, you have to go here: https://my.ooma.com/products/addons_details/port
After the number port is done, you don't have to do any disconnecting of your house wiring from the telephone company unless you want to use your house wiring to distribute your Ooma dialtone. If the phone connected directly to your Ooma meets your needs, then no further action is required.
If your question is if Ooma's wall port is connected to your house walljack, will you receive landline calls on the phone connected to your Ooma, the answer is no unless you are in landline integration mode (use your own number with Ooma) or your internet goes out.
Since I think you signed up in standalone mode (you got a number from Ooma when you activated), it is best to keep the 2 lines separate. Plug a phone in Ooma and plug another phone in your house walljack. If you only have 1 phone, then connect the phone to AT&T, do call forward (if you can do this) so that you can just use the phone connected to Ooma.