In Apple's iPhone Manual (page 170)
Radio Frequency Interference (RFI)
Observe signs and notices that prohibit or restrict the use of mobile phones (for example, in healthcare facilities or blasting areas). Although iPhone is designed, tested, and manufactured to comply with regulations governing radio frequency emissions, such emissions from iPhone can negatively affect the operation of other electronic equipment, causing them to malfunction.
Turn off iPhone or use Airplane Mode to turn off the iPhone wireless transmitters when use is prohibited, such as while travelling in aircraft, or when asked to do so by authorities.
Medical device interference
iPhone contains components and radios that emit electromagnetic fields. iPhone also contains magnets and the included headphones also have magnets in the earbuds. These electromagnetic fields and magnets may interfere with pacemakers, defibrillators, or other medical devices. Maintain a safe distance of separation between your medical device and iPhone and the earbuds. Consult your physician and medical device manufacturer for information specific to your medical device. If you suspect iPhone is interfering with your pacemaker or any other medical device, stop using iPhone.
Not a medical device
iPhone and the Health app are not designed or intended for use in the diagnosis of disease or other conditions, or in the cure, mitigation, treatment, or prevention of disease.
If you have any medical condition that you believe could be affected by iPhone (for example, seizures, blackouts, eye strain, or headaches), consult with your physician prior to using iPhone.
Do not charge or use iPhone in any area with a potentially explosive atmosphere, such as a fuelling area, or in areas where the air contains chemicals or particles (such as grain, dust, or metal powders). Obey all signs and instructions.
When you perform repetitive activities such as typing or playing games on iPhone, you may experience discomfort in your hands, arms, wrists, shoulders, neck, or other parts of your body. If you experience discomfort, stop using iPhone and consult a physician.
This device is not intended for use where the failure of the device could lead to death, personal injury, or severe environmental damage.