The 4th movie has been confirmed by Fox
http://www.deadline.com/2013/06/fox-dates-frankenstein-chipmunks-4-sets-2017-2018-animated-slate/
At this time the title is tenetive and likely to change and the only other thing we know is the release dat of December 11th 2015 but at least Foxx finally confirmed the 4th movie is in the works. I am sorry for this blog being a bit short as it is 3a.m. here but I wanted to make the announcement before I go to bed and forget about it. So now there is both a new cartoon series and CGI movie in the works but neither has many details at this time. On a bit of a side note since we only know the release date please do not go and create an article about the 4th movie yet. If no one else gets to it I will add a small part to the Chipwrecked page mentioning a sequel after I get some sleep since there is not enough information to even create a stub at this point.