On September 7, 2012 NANPA announced the introduction of a new area code for the Canadian province of Saskatchewan starting May 25, 2013. The new 639 area code will overlay existing area code 306 currently serving the aforementioned province (Saskatoon, Regina, Yorkton, …).
Starting February 25, 2013 carriers in the 306 area will be able to play a network announcement notifying callers dialing just the local 7 digit number that the call they have dialed must now be preceded by a 3 digit area code. However, these calls will still be completed without adding the area code until May 25 when 10 digit dialing becomes mandatory.
Starting May 25, 2013 all calls in the newly created 306/639 overlay complex dialed with just 7 digits will be preceded by a network announcement informing the caller that they must hang up and dial the call using 10 digit dialing.
See NANPA official announcement (PDF document):