Number transfers refer to porting a number from an existing phone from one provider to another. This means closing the old phone account and opening a new one with the current provider. For a person or business, this process is permanent and should be considered a committed move to the new provider.
Some service providers charge to port an old number to a new phone, however, this service may also be offered for free at the discretion of your new provider. Call them and inquire about the process of number transfers and whether there’s a small fee.