How to disconnect 2 iPhones from each other?

My mum recently got the iPhone 5 and gave me her old iPhone 4. I recently just got a sim for this one and deleted her old contacts on the iPhone 4, but it deleted all of them from her phone as well. How do i just completely disconnect the iPhones from each other?

You need to set up a separate iTunes account for yourself, with your own email, password etc. Sign out of your mum's iTunes account on the phone, and on the computer, and set up a new account with your own details. Then, you can add your own phone numbers, emails, music, applications, etc, using your new account.

If you want to buy any apps you will have to add a payment method, such as a debit/credit card or iTunes voucher. If you don't want to add a payment method, and only want free apps, follow the information below:

http://support.apple.com/.../kb/ht2534

What if you already did and disconnected it from icloud and the contacts are still connected?

My aunt gave me her old iPhone 5s and we factory reset the phone changed icloud accounts and iTunes accounts and it says we arn't connected anymore and we have different numbers but anytime I add a contact it adds to hers too or anytime I deleted one it deletes on hers and vise vera

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