There is no universal rule regarding this matter. Retailers
will vary on how they implement number transfers. Some retailers will require you to transfer your number while placing your order for a new phone and they will not allow you to do so once the order has been completed.
Other retailers may allow you to transfer your number at a later date – but even then some of them may place a time restriction on when you can do this (e.g. the first month of the contract
). Other retailers or networks may allow you to transfer your number at any point.
To complicate matters some retailers may have different rules in place for different networks, allowing you to transfer your number at any point for one network while requiring you to provide a PAC code during the order process for another network. There may even be some networks that certain retailers will not allow you to port a number to.