Yes essentially that's right.

If WIFI is on then the light goes out which does not mean it will not receive calls. It only means that 3G data isn't being used.

When NZFINEST rang me the device connected light came straight on and calls were coming through the SureSignal even with wifi on.

Stupidly on my part I took the light to mean "device connected and can now be used" what the light actually means is "Device in use"