Someone has raised the point of you should dial 112 instead as the emergency services can track you via satellite through the 112 number, but they can't if you dial 999.
A mobile phone can't use satellite communication so it can't be tracked using satellites, emergency services track it using triangulation from cell towers. Theoretically if you had GPS enabled the phone could send it's location to the cell phone towers, but satellites wouldn't be tracking it because GPS is a totally passive system.

