I am currently researching ways to do this too. Here are a few options I have discovered.
1. GuiXT mobile app - Free to download and easy to setup up. The UI looks the same and you need to validate that your transaction codes work. I have only tested on my iPad but it works. SAP tcode double click works well with touch. You should also confirm that you have GUI for HTML enabled.
2. SAP Launcher mobile app - It costs .99 to download but is easy to setup also. The double click touch doesn't work well and not all tcodes work.
Overall, I like GuiXT much better and they offer consulting services to further customize the UI to enhance the customer experience. I am following more of a phased approach. Phase 1- offer the same SAP UI on mobile devices. Phase 2 - enhance UI. SAP also offers numerous UI tools that should be looked at when you start looking at enhancing the SAP UI.