My iPhone 4 is about 15 months old now and the screen has completely lost the oleophobic property is had when it was new: finger smears now show up just like they do on other phones. Contrary to the comments on this question I've never cleaned it with any sort of solution: all it's ever had is the occasional wipe with a cotton cloth (well, T-shirt :), although of course it will also have been rubbed in the pocket of my jeans. It's never had a screen protector but is completely unscratched and undamaged.
So it seems the coating does wear off over time without using any kind of chemical agent. My question is, is it possible (either at Apple, a third-party service centre or at home) to re-apply it and get the screen back to its fresh-from-the-box state?
Best Answer
No. The organic material is applied during assembly. I'm not aware of any place that can "replenish" the lipophobic substance.
Apple has this to say:
"Please note that the ability of this coating to repel oil will diminish over time with normal usage, and that rubbing the screen with an abrasive material will further diminish its effect and may scratch your screen."
Source: http://support.apple.com/kb/ht3226
You can, however look into replacement covers that also contain lipophobic properties: http://www.mobimega.com/sgp-steinheil-ultra-oleophobic-screen-protector-for-iphone-4.html
Or pay for a new glass screen. Warranty will generally not cover this, but you can always ask for a quote from Apple service in or out of coverage.