What to do before selling or giving away your iPhone, iPad, or iPod touch

Make Sure Delete Everything Permanently from iPhone Before Selling

Follow steps to remove your personal information from a device you're giving away, even if you don't have the device anymore.

If you still have your iOS device
Before you sell or give away your device, you should remove your personal information.
You shouldn't manually delete your contacts, calendars, reminders, documents, photo streams, or any other iCloud data while you're signed in to your iCloud account. This would delete your content from the iCloud servers and any of your devices signed in to iCloud.

Warning by CNET: iPhone "Restore" does not delete personal data!
If you restore factory setting for your iPhone,it does’t mean “Erase” all iPhone data permanently,becuase some recovery software can restore them easily,you need to use a third-part eraser tool to wipe iPhone data.

Erase All Data on iPhone before selling

In this article, we mainly talk about the iPhone Data Eraser, which is specially designed for iPhone users who want to resell their iPhone devices. You just only need to perform one click, your iPhone will be erased clearly and all existing or deleted files will be overwritten by junk data at the same time. That will promise nothing can be recovered after the erasing job. It is quite easy to use. All you need to do is run the software, connect your old iPhone and begin to erase it. Everything can be erased from your iPhone, including contacts, SMS, phone numbers, user names, passwords, emails and many more.

An easy way to solve this problem is to delete all junk files on iPhone permanently and speed up your iPhone. However, this method is not safe as it seems. Actually, deleted iPhone contacts,sms,photos,videos and other files are still stored on the device unless new data is written to the same piece of storage. The photos can be restored with the help of certain data recovery software. To erase iPhone data permanently, you should use iPhone Data Eraser instead. iOS Data Eraser is a powerful and easy-to-use data wiping program designed for the purpose of data deletion on iOS based devices. It’s the ultimate solution to erase all contents on iPhone permanently and the data is no longer recoverable.

Follow these steps:
Back up your device.
Tap Settings > iCloud. Scroll down and tap Sign Out. In iOS 7 or earlier, tap Delete Account.
Tap Sign Out again, then tap Delete from My iPhone and enter your password.
Go back to Settings and tap General > Reset > Erase All Content and Settings*. In iOS 7 or later with Find My iPhone turned on, you'll need your Apple ID and password.
If asked for your device passcode or Restrictions passcode, enter it. Then, tap Erase [device].
Contact your carrier for guidance on transferring service to a new owner. If you aren't using a SIM card with your device, you can contact them to get help transferring service to the new owner.

If you no longer have your iOS device
If the steps above weren't completed and you no longer have your device, follow these steps:
Ask the new owner to erase all content and settings as described above.
If you're using iCloud and Find My iPhone on the device, sign in to icloud.com/find, select the device, and click Erase. After the device has been erased, click Remove from Account.
If you're unable to follow either of the above steps, change your Apple ID password. This won't remove personal information that's stored on your old device, but it will prevent the new owner from deleting your information from iCloud.
If you're switching to a non-Apple phone, deregister iMessage.
If you're using Apple Pay, you can remove your credit or debit cards at iCloud.com: Choose Settings to see which devices are using Apple Pay, then click the device. Next to Apple Pay, click Remove.

Permanently to Erase iPhone Data on Computer or Mac

First of all,free downoad the ios data eraser:

 

Step 1. Run the Program and Connect iPhone to PC

Step 2. Choose Files You Want to Erase and Wipe Mode

Step 3: Start to Delete Data from Your iPhone
Finally, you can choose the option of erase all data and settings to delete all text messages, including SMS attachments from your iPhone 5S/5C/4S/3GS.
Done! You have successfully got your iPhone to a clean slate. Want to delete iPhone files permanently to protect your personal information from revealing? iPhone Data Eraser is your good assistant.

Learn more

How to erase photos from iPhone before selling

how to erase iPhone messages before selling

how to delete contacts on iPhone before selling

*When you tap Erase All Content and Settings, it completely erases your device, including any credit or debit cards you added for Apple Pay and any photos, contacts, music, or apps. It will also turn off iCloud, iMessage, FaceTime, Game Center, and other services. Your content won't be deleted from iCloud when you erase your device.