If you want to flash your ZTE device to PagePlus, navigate to the official web page, fill up the Page Plus Cellular Activation form (make sure you select Phone from another carrier (Sprint/US Cellular/Virgin/etc.) from the What kind of phone drop-down list), enter the 15 digit IMEI number of your device, select a Page Plus monthly plan you want to activate and click the red button.
Note: You can find the IMEI number of your phone if you're dialing *#06#
.