An account Key gives user access to email account without entering password. Account Key generated once cannot be used second time. It is Valid for only onetime login.If you have brought a new mobile set and have access to old phone as well. You can use Keys generated on older phone to access Yahoo mail on new phone. The procedure to get Yahoo Account Key on new phone with the help of old phone.
1. Install the same code generating Yahoo App on new phone which you were using on old phone
2. Open the Application and Tap on Sign-in
3. Now enter your Username in the given field
4. Click on Continue
5. The next page will prompt you to enter an account Key
6. Now refer to your old phone and tap Account Key icon
7. It will open a page that shows Account Key
8. Enter this Key on new phone and click on Sign in
9. Now your new phone should start receiving Account Key notification!
10. Now if you are planning to reuse old phone, sign-out from your Yahoo App and reset your phone in Settings.