After departing Canberra from runway 35 at 0744, the aircraft was observed by radar to correctly follow the assigned standard instrument departure. However, the pilot failed to transmit a departure report on departures frequency 125.9 and contact could not be established on tower, departures, approach or sector frequencies. At 0749 an uncertainty phase was declared. The aircraft was observed to be following the cleared route, Canberra to Bindook via Cullerin and at 0756, the pilot contacted Sydney arrivals and requested descent. The uncertainty phase was then cancelled by Sydney Control. The crew of VH-TJO were interviewed by the company training manager, and although the captain could not specifically recall contacting Canberra Departures, it appears that the Sydney FIS frequency 125.7 mhz was incorrectly selected in lieu of 125.9 mhz. When a descent clearance was requested Sydney FIS directed the crew to the correct frequency.