You can get the free reader
here. It only includes the King James version. Olive Tree regularly runs specials and often gives away Bible versions. In the last 18 months they have given away the ESV and NASB. You can register and received notifications of their sales. They often have 25% off sales of everything at their website.
Once you have the free version installed and you have registered, adding books and Bibles is very easy. You can purchase from within the app or their website and download later.
[EDIT]
I didn't notice you said you had an iPhone. The link is to the android store. Everything else is said is likely true for the iPhone app.