sms messaging with iPhone X

Hi

It may help to follow the instructions here, including under the heading "Get help if you can't send or receive messages" and including unpairing and re-pairing your Apple Watch if necessary:

Read and reply to messages with your Apple Watch - Apple Support

And to check that you have followed the instructions here:

• Switch your Apple Watch to a new iPhone - Apple Support
• Set up and use cellular on Apple Watch Series 3 (GPS + Cellular) - Apple Support

Keep in mind that the functions that are available on your Apple Watch when it is away from your iPhone depend on various factors including:

• Your Apple Watch model:

  Apple Watch - Compare - Apple

• The features of your carrier service plan:
  • Apple Watch - Carriers - Apple
  • Make a call with Wi-Fi Calling - Apple Support
• The type of connectivity that is available to your Apple Watch at the time:

  About Bluetooth, Wi-Fi, and cellular on your Apple Watch - Apple Support

Features and requirements that apply under various circumstances are detailed here, including within the footnotes:

How to use your Apple Watch without your iPhone nearby - Apple Support

If you still need help, then I suggest that you contact your carrier in the first instance. If the issue persists, then, depending on your carrier's advice, I suggest that you next contact Apple Support (remote diagnostics and/or mail-in service may be available, if required), make a Genius Bar reservation or visit an Apple Authorised Service Provider for assistance:

• US: Apple Watch Service Answer Center - Apple Support
• Elsewhere: Apple - Support