Best answer by BobTheElectrician
If you sign up for a new provider and port your existing number to your new "other" phone, your Koodo account will automatically be cancelled and you will be billed for your balance, if any, plus any overages, assuming you are on monthly. If you are currently on prepaid, you will lose whatever is left on your time and boosters.
If the idea is just to make your old number available to older contacts at minimal cost, then port it to CallCentric or another Voip provider, and have those calls forwarded to your "new" Koodo number for a penny or two a minute.
Probably best to call *611 and establish a second line on your account with the new number before porting out through them and cancelling the original service.