Considered TapaTalk but the problem is that not everyone wants a mobile app. Not to mention, you'd have to pay $3 for that.
MSH 3.0 will have a mobile skin, and Invision has a mobile app that goes with it available for free in the App Store for iPhone. The mobile skin (w/o the app) can be optimized to whatever user agent comes up when you visit MSH on your phone, and is fully usable (PMs and posting). Also, if you are one of those who wants the full-fledged experience, you will have the ability to switch skins to standard while on your phone.
So, in a nutshell, we've got this covered.