Although ZTE can sell its products to the civilian consumers all over the US, a recent bill that was signed by Donal Trump bans the government use of any device made by the Chinese brand due to security issues. Even more, this bill also forbids the use of Huawei hardware for the same reason.
https://www.notebookcheck.net/No-Huawei-and-ZTE-handsets-for-the-US-government-decides-President-Trump.323052.0.html
It is really scary what Trump is doing. Steel, aluminum, smartphones...
If he keeps it up like this, the US might start making smartphones again. Remains to see how it all turns out. At least you can buy a ZTE or Huawei for personal use...