Yes correct. You can port your existing number and do it all online on the birdie website, you enter a start date/time and they will take care of the transfer for you. Mine will be effective 1st April between 1am and 4am. Will report back here then if any troubles.
Just make sure your old number is out of contract already or you will run into issues.
Also if you stop and continue later on, I doubt you can keep the same number again.