Public Mobile customers can change their phone numbers without charge.
Log into your self-serve account, and click the Plans and Add-ons tab. Several sub-tabs will appear. One of them will be Change Phone Number. Choose the province and city where you live, and 5 random numbers will be presented to you. If a number appeals to you, choose it. If none appeals to you, don't choose any; instead, return in a few days when the selection might be better.