[shawnreilly]

The first thing I would do is think about what capabilities you need in order to successfully execute the product, and equally important how you would want to distribute the product. Depending on the answers, I would then find a framework (or multiple frameworks) that facilitate the approach you want to take. This will allow you to prototype faster (and reiterate faster as you learn from your customers). This would also play in to how you approach building the back end.

From reading your replies to other comments, it sounds like you want access to a phone's local resources, and you are possibly interested in using web technologies. I would look into Apache Cordova (aka PhoneGap) or something similar (there are many). This allows you to build once with HTML/CSS/JS, and then distribute via Android/iOS and more (differentiation being each platform would need specific front end JS code to access the phone's local resources). This approach is commonly used in conjunction with a back end that accepts API Requests (aka front end makes Ajax request, back end responds with Data). I'm using this approach for one of my current projects.

[abhimskywalker]

I agree with the above, and additionally you can check out http://ionicframework.com/ to build once for web (with backend REST API) and then port it to iOs and Android pretty easily. They offer nice-looking UI elements as well specially suited for mobile use cases. I found porting a simple angularjs based webapp to android and iOs pretty easy (thought only tested it as development prototype). Should be worth checking out.