Remove Sensitive Data From Work Phone
One more hint is Nuke My Phone:


  Nuke My Phone protects your privacy by secure deleting your personal data, such a photos and videos, and returning your phone to factory settings. Now you can safely repurpose old devices or upgrade your current one without worrying about unauthorized data recovery. Nuke My Phone delivers the peace of mind that comes only from knowing your personal data cannot be compromised.


Works directly on the device.