The solution I use is a free app named SimpleNote. It syncs with the web (simplenoteapp.com), and in turn syncs with a desktop widget on my Mac. So any notes I create on my iPhone appear on my Mac, and vice versa. I've installed SimpleNote on my wife's iPhone as well (synced to the same account). So all of our notes automagically are kept in sync on both iPhones, and on our Macs.
Another approach is the PlainText app. It syncs with Dropbox -- each PlainText 'note' is a text file in a Dropbox folder. Similar to SimpleNote, this gets your notes onto your desktop (either Mac or PC), and you can then sync with PlainText installed on another iPhone.