The Inmarsat constellation has been upgraded over the last 12 months...
On this subject:
By now pretty much every spook in the Sahara knows not to use Inmarsat or Thuraya satphones for communications, as very soon after the first ringtone they will receive an air delivered parcel courtesy Uncle Sam from one of those Predators circling somewhere overhead... The In Amenas attack was planned and executed using old cellphones and local scratchcards for this reason.
So yes, signal location may be traced to within a few metre accuracy.
If this technology will actually help find the missing aircraft, it will be one of the rare proven benefits gained from the hundreds of billions spent post 9/11 on clandestine surveillance.