I've been using the out of the box Facebook app and I am able to view my inbox. I think it's under notifications. If not, then it's under profile. I've also found the Facebook Mobile page is really helpful, find it in your browser. The key so far to Facebook chat though, is Meebo. I'm not the biggest fan on it, and am hoping for an official app to come around, but Meebo gets you online and will sync your other accounts like AIM as well. Pretty helpful.