In the second floor of Mall Paseo Costanera, you can "grab" the signal from the Telefonica del Sur stand, located near Heladeria Sabory. It's an un-protected net and it's name is "WiTv_Telefonica_del_Sur"
Wireless: free
Food: Variety of hot food
Hours: Mon-Sun, 9:30am - 10pm
In the food court of "Mall Paseo del Mar", you can get the signal from "MuniPMTT_WiFi" which belongs to Ilustre Municipalidad de Puerto Montt (or Highest City Council of Puerto Montt).
So far, the network is working. Dunno if its a summer test or it will last all throught the year.