Lost Sprint phones can be located using the Sprint Family Locator service. The official entry on the topic on the Sprint Support portal lists that the phone must be turned on and a Sprint network covered location to be locatable.
The supplied location is approximate, achieved through the triangulation of the phone location using Sprint network towers. A reference address is also supplied. Sprint instructs users not to go looking for lost phones in unfamiliar locations themselves, advising them to go only to locations that they have recently frequented within the supplied reference area.
The Sprint Family Locator service is only available to the official account holder of a lost phone. Although the Family Locator app is available on both the Play Store and iTunes, users need not have the app installed for the service to work. To start using the Sprint Family Locator application, users should navigate to the Family Locator Signup portal, where they are instructed to enter their account’s primary account holder number and their email address. They are then instructed to enter security information to confirm their identity as the primary account holder. Next, a choice of phones to locate is presented. Finally, the account information and terms of service are shown before the location service is activated.