This add-on is available for Android devices, Apple devices, and wearable devices. Here is more info from AT&T’s website on how this add-on works for each device category:

AT&T Number Sync Blocker for Android

Want to keep devices from syncing to your Android tablet? Add this free feature to each device you want to block.

• Prevent the use of NumberSync for a number on your account.
• Add this free feature to each Android device you want to block

AT&T Number Sync Blocker for Apple

• Prevent a number on your account from using NumberSync.
• Add this free feature to each iOS device you want to block.

AT&T Number Sync Blocker for Apple Watch (Cellular)

• Keep your Apple Watch (Cellular) from syncing with an iPhone on your account.

AT&T Number Sync Blocker for Wearables

• Keep your watch from syncing with a phone on your account.