create a 3d shapefile ?

Is it possible to write point ESRI shapefiles with x,y,z
coordinates using writeOGR()?
According to what I've been able to find, it seems
that spatial points can have 3 coordinates while
spatial lines cannot. Nevertheless, coordinates() accepts
2 arguments (x,y) only. So actually, do not know how to define
x,y,z coordinates for spatial points (data frame) objects.
Is it possible?

Thanks,

Agus