According to the Bank of Zambia’s Currency Rebasing Technical Guidelines dated August 2012, the new currency (ISO code ZMW) will be introduced 1 January 2013, and old notes will cease to be legal tender as of 30 June 2013, but may be exchanged at the Bank of Zambia until 31 December 2015, after which time they will be demonetized.
This presentation to commercial banks provides additional interesting information.
Courtesy of Tod Hunt.