NumberSync for compatible Apple Watch (GPS + Cellular): To access the AT&T wireless network, complete NumberSync setup and sync your watch with an HD-voice activated iPhone. 

Talk/data charges: Calls to international numbers using NumberSync are subject to international rates consistent with your plan or international option. When your watch isn’t connected to Wi-Fi or Bluetooth, talk and data charges apply to usage over the cellular network. Those charges will count against your wireless data allowance for your watch. Watch doesn’t support roaming.

SMS/MMS: Text messaging requires that your synced smartphone must be powered on so SMS/MMS messages may be forwarded to your watch. iMessage must be enabled and your smartphone must be connected to our network through either a cellular or Wi-Fi connection. If using a Wi-Fi connection, your smartphone must have Wi-Fi Calling activated.

911 calls: If you can’t be located using location information obtained from your watch, 911 calls will be routed based on the address you provide in the NumberSync settings of your watch. 911 calls aren’t supported outside the U.S., Puerto Rico, or the U.S. Virgin Islands.

TTY limitations for 911 calls & Real-Time Text: Due to technical limitations, NumberSync can’t be used with TTY devices or Real-Time Text. Persons with communications disabilities can still reach 911 services by either: (1) calling 911 directly using a TTY over the cellular network or from a landline telephone, or (2) sending a text message to 911 directly (in areas where text-to-911 is available) from a wireless device, or (3) using relay services to place a TTY or captioned telephone service (CTS) call from a wireless phone over the cellular network or from a landline telephone, or (4) using relay services to place a IP Relay or IP CTS call over a cellular data or other IP network. View RTT progress. 

Additional restrictions: You can’t use NumberSync to call 211, 311, 511, or 811. Not compatible with Smart Limits, Ringback Tones, OfficeDirect, or OfficeReach.