Published: November 08, 2011
A new area code was recently announced for the Western Quebec communities of Drummondville, Gatineau, Sherbrooke, Trois-Rivieres and more. The new area code 873 will become active on September 15, 2012 and will cover the same geographic area currently served by area code 819. With the introduction of the new 873/819 overlay complex this area will use 10 digit dialing for local calls. I couldn't find any details in the official announcement regarding a permissive 7/10 digit dialing period (a 3 month or more permissive period is generally used before an overlay area code is introduced; this way people can get used to dialing 10 digits instead of 7).
See the official NANPA announcement and map of the new area code (PDF document).
Visit area code 873 page for a list of cities served, map and other info.