navigator.network.connection.type returns 'unknown' when the device is just started. When you change the network type (for example when you turn Wifi on and off) the type is correct. But if a user never does this it keeps returning 'unknown'.
We use this to detect if data can be sent or not, and when it returns 'unknown' it's possible that there is a connection, but it's possible that there isn't one too. We can't know which one it is.
This happens with PhoneGap 1.4.1 on Android 2.2.2 and 2.3.3, on iOS it seems to be correct.