To retrieve erased contacts from a smartphone, plug the phone into a PC and restore the phone to its most recent backup. If no backup is available, downloadable software such as Android Data Recovery or iPhone Data Recovery can recover contacts still stored on the SIM card.
As of 2015, most smartphones can be plugged into a computer, and a backup of the phone's memory can be created and stored on PC or Mac. Smartphone users should back up their phone's memory regularly, particularly after adding important contacts. If a backup was created before the contacts were lost, restoring the phone to its most recent backup restores the contacts. Other data such as text messages and photos that were added after the backup are lost when the phone is restored.
Android Data Recovery is a free app that can be downloaded from Android Recovery. Once the software is downloaded, plug the phone into the computer and follow the onscreen instructions to restore deleted contacts. Similar software is also available for the iPhone. If the user does not wish to download software, he may need to take the phone back to the manufacturer or point of purchase to seek professional assistance.