Apple Watch Series 4 (GPS + Cellular) requires an iPhone 6 or later with iOS 12 or later. Apple Watch Series 4 (GPS) requires an iPhone 5s or later with iOS 12 or later. Wireless service plan required for cellular service. Apple Watch and iPhone service provider must be the same. Not available with all service providers. Not all service providers support enterprise accounts or prepaid plans; check with your employer and service provider. Some legacy plans may not be compatible. Roaming is not available. Contact your service provider for more details.