There are a variety of locations to find a user manual for ZTE phones, including directly from ZTEdevice.com or from the cell phone service provider. Although the ZTE website has support manuals for all of its products, only supported device manuals are available via the cell phone carrier.
As of November 2015, both AT&T and Sprint have user manuals available online for supported ZTE products via their respective websites. If you're an AT&T customer, visit the Device How-To Center at att.com to identify the specific ZTE product in question, then click User Manual to download a PDF version of the manual. If you're a Sprint customer, visit the Devices support page at spring.com to identify the product, then navigate to the Troubleshooting section and click User Guide.