If you wish to download a copy of Oedipus Rex to your phone or tablet, you may find copies here:
Project Gutenberg (links to .html, .epub, and Kindle-formatted versions)
Oedipus Rex for Kindle ($.99 charge)
Oedipus Rex for Nook ($.99 charge)
Download or listen to a streaming audio version of the play at Librivox.
The full text of the play may be read online here.
Another translation of the play may be read online here.