Yesterday (2009.02.05), Google announced:
Today we are excited to announce the launch of a mobile version of Google Book Search, opening up over 1.5 million mobile public domain books in the US (and over half a million outside the US) for you to browse while buying your postage.Interesting... As noted on Yahoo Tech news, this poses something of a challenge to Amazon's Kindle reader. (Also note the other free ebook apps for iPhone mentioned there: Stanza, eReader or BookShelfLT.)
While these books were already available on Google Book Search, these new mobile editions are optimized to be read on a small screen. To try it out and start reading, open up your web browser in your iphone or Android phone and go to http://books.google.com/m.
I did check out the mobile Google book site, and there is a whole section on Religion with the usual suspects of public domain books. There are a number of Greek texts such as Winer's 1874 Grammar or Souter's 1913 Text and Canon of the NT or Goodwin's 1860 Syntax. To keep things efficient for a mobile device, everything has been rendered with OCR, but in the instances with Greek, note that you can click on the paragraph to have the original appear as a graphic. (Cf. the graphic below with the image of the Greek and the confused Greek OCR below it.)
In any case, it's all free and may prove helpful to you.