While true in terms of answering
@ElbowsLow's question, do remember this is not universally true in the global scope. There are a couple different models with different 5G/LTE bands split up by different countries.
Until recently there were also different models for different carriers within the US, though it was more a CDMA/GSM split. The progression though has been towards unified models and the landscape is much better now than it used to be.
See:
See the countries and regions that have certified 5G and LTE networks on iPhone including the U.S., Canada, Japan, Germany, China mainland, and more.
www.apple.com
If you plan to import the new iPhone XS or XS Max across borders, you may want to think twice. There are four different models of the iPhone XS and XS Max being sold in different countries, and they have slightly different LTE band support.
www.pcmag.com