Apple posted their iPhone Out-of-warranty Battery Replacement Program Frequently Asked Questions page.
The page states that Apple will replace your battery if the iPhone's ability to hold an electrical charge has diminished.
"The program costs $79, plus $6.95 shipping. The program cost is $85.95 per unit.
All fees are in US dollars and are subject to local tax. Service may not be available if your iPhone has been damaged due to accident or abuse."
The service takes three business days to perform. Additionally you may get an AppleCare Service Phone for $29 while your phone is being repaired. Details are here.
At first we thought the document pointed to a new tech note about optimizing battery life, but it just pointed to the older iPod version.
