Capcom have revealed that Gyakuten Saiban 5 ( thats Ace Attorney 5 to us in the west) will be the first game in the series to feature voice acting. 
In an interview with Japanese magazine Nintendo Dream, translated by Sillconera. Capcom explained that after “much consideration”the decision was made to enable the game to work with the anime cut scenes included in the game that would also feature voice acting. This also enabled the team to overcome ‘tuning difficulties’ they faced when trying to convert the old soundfiles used from previous Ace Attorney games for use on the 3ds.
Ace Attourney 5 is due for release in Japan in 2013 with a Western release to follow afterwards.