Hi, I’m currently in the US & want to buy a Apple Watch 3. However, I live in the UK & have a iPhone contract with EE. If I buy the Apple 3 watch device with GPS & 4G in the US will I be able to use it fully in the UK?

Hi

Apple Watch Series 3 (GPS + Cellular) is not locked to any specific carrier and has a built-in eSIM that copies information from the iPhone's SIM card.

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).

If buying Apple Watch Series 3 (GPS + Cellular) in another country, then you would need to buy a model that supports the relevant LTE and UMTS bands for your intended country of use and your supported carrier there.

There are three different regional versions of Apple Watch Series 3 (GPS + Cellular), each supporting different LTE and UMTS bands, as detailed here - including different models for the UK and US:

Apple Watch - Carriers - Apple

If in doubt, I suggest that you contact your intended carrier to ask whether any given model can be used on their network with a plan that they offer for iPhone that supports Apple Watch Series 3 (GPS + Cellular).

The built-in cellular features cannot be used when roaming. Also keep in mind that warranty service availability may be restricted.