@BOAC, I can't remember where I saw it, but there was a report that other flights were in the area at the time, both ahead, behind and parallel - if memory serves, one was a DHL freighter. The report also said that none of the flights that might have heard from AF447 picked up anything. It does seem a little puzzling that the crew sent out an ACARS message but no radio traffic was heard, although the fact that the first ACARS message was sent on the hour suggests it may just have been a SOP-scheduled message.