If you have a iPhone then you can assign a photo or a ring tone to any of your contacts. With this feature you can know who is calling just by the sound of the ring tone or by seeing their picture if the phone is in silent mode. To do this open the contact and tap on the edit button at the top right corner. Now tap add photo. This allows you to take a new photo with the integrated camera or choose a new photo from your library. To assign a ring tone tap assign ring tone and choose the tone from one of the available tones. In this way you can make your iPhone more personal. This video shows how to assign a photo or a ring tone to your contacts in iPhone.