Indonesia Air Asia’s 22nd A320 will arrive in Jakarta soon. The latest, PK-AXW with msn 5137 was recently spotted making its first flight on 24th April 2012:
First Flight of Indonesia Air Asia’s 22nd A320 (to be 19th in current ops)
 
Indonesia Air Asia currently operates 18 A320s. Towards the end of 2011, 3 new A320s on lease were sent to Malaysia Air Asia (PK-AXN, AXO, AXQ) in exchange for 4 “old” A320s (PK-AXR, AXS, AXT, AXU) from the latter, sold to Indonesia Air Asia, to comply with the regulations in force beginning 1st January 2012, where airlines must have 5 owned aircraft and at least 5 more leased aircraft. But don’t worry, the oldest one is from as late as 2006.


(Thanks to @arifmuharram for the heads up!)