Until the ZX Spectrum Next Kickstarter delivers several thousand Nexts to backers, there aren't that many people with real hardware who can run NXtel in its native environment yet. Because the Next platform is new and still evolving, emulator support for the Next is still in development too. Currently, ZEsarUX and CSpect are the two crossplatform Windows/MacOS/Linux emulators offering Next support in varying degrees.
For an emulator to be able to run NXtel, it needs to support the Next serial UART or the ESP 8266-01 wifi module.
ZEsarUX does not yet have any UART emulation.
CSpect emulates the Next wifi module from version 2.7.0. See Using NXtel in CSpect for instructions.
Zeus is a fully-functional development assembler, IDE and emulator, running on Windows. It also has UART emulation in it's experimental build. See Using NXtel in Zeus for instructions.