From what I've read, the mother reported him missing back in 2010 to the child welfare authorities, but not the police. She is an immigrant and possibly didn't know the procedure and thought the welfare authorities would contact the police.
When the boy got the phone, he immediately texted his mother in Florida.
The police in Clayton County, where he was held, were never notified of a missing child.
The woman arrested with the father, Samantha Davis, is currently on probation for a previous child endangerment charge.
This article gives a good summary of the facts, and paints a better picture of how and why it happened. It doesn't contain all the facts that I've come across, but it puts the story in perspective and makes it more credible.
http://www.nydailynews.com/news/crime/watch-boy-found-behind-wall-made-work-roof-article-1.2028732