In current kontact mobile version it is not possible to determine the actual online status of a resource. Version 4:4.5~20100917.1177596-1maemo3.1174921
In version 4:4.5~20101013.1185418-1maemo1.1185177, there is an indicator to at least show general online/offline/synching status.
Should be closed - is fixed
The account tab now also has a per-resource status indicator.
(There with n900 and ce for a while.)