Apple doesn't do any repairs except for replacing the battery when requested for an iPhone no longer under warranty. Service is just a generic term for inspection and testing with a hardware diagnostic check run on the iPhone. If a hardware component has failed with an iPhone under warranty that is covered under warranty - not due to abuse or accidental damage, the iPhone will be exchanged. An exchange under warranty will be a new or refurbished iPhone with no way to tell the difference. If refurbished, a refurb gets a new battery and an entirely new exterior. All other components are inspected and tested being replaced as needed. Since an exchange under warranty - called a service unit regardless if new or refurbished are in stock, it is faster to exchange the iPhone with a service unit than doing individual repairs for each warranty claim - the turnaround time under warranty to get a working iPhone or working properly is faster with a service unit exchange than with differing and individual repairs.