If you're really serious about it and are willing to put in some time to actually learn to program in Cocoa, the way I would do it would be a combination of reading all the stuff Apple has to offer along with a couple good books both for reference and more conceptual big picture/getting into the Cocoa mindset stuff.
If you just want to try to hack something together that works than you'll probably do best with a combination of Apple's sample code and lots of questions on various forums when you get stuck.
The books I would recommend would be Programming in Objective-C, by Stephen Kochan and Cocoa Programming for Mac OS X, by Aaron Hillegass. The former is a good introduction to the Objective-C language itself, and the latter is pretty much the Cocoa book. It's not an iPhone specific book, but pretty much everything in it (especially the concepts and design patterns) still apply. Keep in mind you wont have access to the garbage collector on the iPhone. You should also be sure to read through Apple's own Introduction to The Objective-C 2.0 Programming Language.
For actual code to look over and adapt to your own needs, it's hard to find anything better than Apple's own iPhone sample code library.
You might also try these two forums for any SDK questions you might have, as well as of course Stack Overflow for the more general stuff that doesn't fall under the NDA.