JD-EE;
The aircraft would be operating well below 10MHz and probably around 5MHz or even 3MHz at that hour of the night in June of 2008.
Just as a refresher, I've thrown some facts together based on what was actually happening at the time -
NOTE : June 2009!
01:31:44 - RECIFE (126.5MHz) gave AF447 the ATLANTICO HF frequencies: 6649 or 5565kHz, then 6535kHz after the TASIL.
01:33:25 - AF447 contacted ATLANTICO on 6649kHz.
01:35:15 - AF447 reported to ATLANTICO that they passed INTOL 0133, at FL350, estimating SALPU 0148 and ORARO 0200. SELCAL - CPHQ.
HF Propogation
At 0200 UTC 2009-06-01 LKP to NATAL (Atlantico/Recife HF)
MUF = 7.0MHz, LUF = 2.0MHz, Solar Flux = 71, Hops = 1, Dist = 592NM.
Primary 6649kHz, Secondary 5535kHz
At 0200 UTC 2009-06-01 LKP to DAKAR (Dakar Oceanic)
MUF = 12.5MHz, LUF = 2.0MHz, Solar Flux = 71, Hops = 1, Dist = 1053NM
Primary 6535kHz, Secondary 5535kHz
Air to Air
The EUR - SAM Pilot to Pilot frequency is 123.45MHz.
The graphic shows the position of all four Air France flights at around 0210, and confirms that AF447 was well within VHF range of the other 3 aircraft.
Summary
Solar conditions were quiet ~ low activity. No lightning was observed by satellite detection, or reported by other flights that night in the Atlantic ITCZ. St. Elmo's fire was reported by a flight, and AF459 did report difficulties on HF, but whether that was due to static or just no reply from the station they called, I do not know.