You can do testing of disconnecting your house wiring from the phone compnay at the NID now if you want.
Look at this post (most people just need to go out and unplug a modular plug): viewtopic.php?t=14206#p99167
Once your house wiring is disconnected from the telephone company, you should find all your house phones dead without dialtone. Then, it is safe to connect a phone cord from Ooma's "phone" port to a walljack. Once this is done, all the house phones should have Ooma dialtone.
You can go back out and plug the modular plug back in to make your landline work again (but make sure you unplug Ooma's "phone" port from the walljack first) or you can start using Ooma right away feeding your whole house (this is only feasible/practical before port completion date if your landline can be forwarded to your temp Ooma number; still while you can receive all your calls, your outgoing callerid would show strange temp Ooma number to people you call).
In any case, you now know what to do after your landline number is ported to Ooma.