In order to climb Villarrica without a guide, not only must you prove IN SPANISH that you are an autonomous climber (e.g. with a national mountaineering federation card with picture), you must also have crampons, an ice-axe AND A HELMET.
Agree on the helmet front. The less snow there is the more chance you have rocks bouncing down from the old lava flows at the summit. Also main route now slightly different as a result of crevasses opening up since early 2010. Gas mask recommended if spending lots of time exploring the summmit area.
To Climb this mountain without a valid CONAF authorization should not be considered a valid option:
Registration allows time alerting and coordinating rescue operations in case of accident. Also it allows control the inexperienced people who want to perform the tour.
There are risks inherent to the mountain that have caused serious accidents, in some cases, foreign tourists have been dead (2012).
Deep crevasses, big rock falls, avalanches and exposure to toxic gases.
Recommend that option is irresponsible.
Only allow you to save a few dollars but will hinder the work of control and commit a criminal offense under the laws of Chile.
There is a control point on the path where companies are checked about the number of people, guides and equipment.
The guides do not accept responsibildades on tourists that have not been properly registered for that tour.
I'll second the comments about the importance of a gas mask if you're exploring around the crater. The smoke is rich with hydrogen sulfide, which turns to sulfuric acid on contact with eyes and lungs. I would not like to experience that again.
To get permission you must show a club membership from a climbing club in your country on paper. You must check in at the CONAF office at the base of camino volcan.(Right before the road turns to asphalt) They do not open until 7am. It is not possible to recieve permission for this climb at the CONAF office in downtown Pucon, although this is a good place for questions. They take the permits seriously. You may be turned around by the top of the ski lift if you did not register at the base of the canyon.This is a very easy climb but it is spectacular with the crater and promenice over the valley. It is also easy to rent gear on the main street in Pucon. May be worth renting a gas mask. The fumes are pretty awful.