Once built a project...

[maiorfi]

...how to upload elf file to device?

[xiongyihui]

We use vxp file instead. Hold the RePhone's button 2 seconds to enter storage mode. The RePhone will act as a USB Storage. Put the vxp file into the storage and edit the file named autostart.txt (create one if not existed). The content of the autostart.txt is like:

[autostart]
App=C:\your_app_name.vxp

[xiongyihui]

Maybe you can refer to the guide - http://www.seeedstudio.com/wiki/Lua_for_RePhone