Same Number, Different Phone
Have you heard of “Mobile Number Portability” (MNP)? This system came into effect one month ago today (on October 24, 2006) and it means that you can keep your phone number even if you change from using DoCoMo to au or SoftBank as your provider. (MNP does not apply to PHS phones, but it can apply to prepaid phones.)
However, it is not as easy as it sounds. You have to cancel your current contract, subscribe to a new contract (both of which may involve fees), and then buy a new phone. Also, while your number won’t change, your email address will.
Here is the procedure for changing your provider without changing your current phone number.
First of all, you have to contact your current provider. From your cellphone, call one of the following numbers depending on who your current provider is.
Your current provider will give you a “reservation number”. Take that reservation number to your new provider. As soon as your new carrier can confirm your reservation number with your current carrier, your current contract will be terminated. You may be charged a “termination fee”. (For example, au charges 2100 yen to terminate a contract.)
Once your contract is terminated, you will have to sign up for a new contract with your new provider and buy a new mobile phone. When you sign up for the new contract, you will be asked for ID, so please bring your driver’s license and your seal (hanko) along with your reservation number. You may have to pay a “subscription fee”. (For example, au charges 2835 yen to new subscribers.)
This will allow you to keep your current phone number, but as I mentioned above, you will not be able to keep your current email address. However, depending on the provider and your old and new phones, you may be able to get your address book information transfered to your new phone. If this is possible, then you can send an announcement to everyone in your address book to say that your address will be changed.
Source: au KDDI site