Buying Apple Watch 3 in Germany and will it work when traveling g to USA

Hi

The built-in cellular features on Apple Watch (GPS + Cellular) cannot be used when roaming.

The built-in cellular features require a carrier plan in your country of use that specifically includes support for Apple Watch, including the carrier activating the device on the plan.

You would also need a model that supports the relevant LTE and UMTS bands for your intended country of use:

Apple Watch - Carriers - Apple

Apple Watch (GPS) models will function as normal, in conjunction with the paired iPhone.

More information:

Apple Watch - Vergleichen - Apple (DE)

Watch - Apple (DE)

The built-in cellular features on Apple Watch (GPS + Cellular) require a compatible plan for the paired iPhone from a supported carrier in the country of use and cannot be used when roaming.