What language/framework is best worth learning for mobile application development? My specific situation is that I'm very familiar with Java and C++ (I especially love Qt), but have limited experience with other languages. Some options I'm considering:

1) Learn Objective-C and all the iPhone-specific tools

I do have access to a mac. The downside here is I'm restricted to the iPhone, so I'd have to rewrite almost everything if I wanted to branch off into another mobile device (or move later to a cross-platform framework). Even after knowing Objective-C, it seems like other frameworks might be more efficient/faster to code in?

2) Use some existing cross-platform framework for development

I've looked at rhomobile, but I only have limited experience with Ruby (and at first glance, it might be a little pricey comapred to other options). Appcelerator also looks popular and nice, but it uses html/css/javascript. Airplaysdk looks good, but it's new and I haven't been able to see much written about it (is it worth going for?).

3) Wait for something better to come along

How far away is Qt for the iPhone? That would be ideal, but it isn't available now.

So what do you recommend? Productivity/efficiency is my top priority, although learning a useful language for the long term would also be okay.

Thanks