Google has introduced a new, free public DNS service which, according to their information page, is intended to:
And so far, they're not even trying to monetize via add placement or site-suggestion. For those whose ISP is simply not performing DNS well, or for anyone worried they may be subject to DNS cache poisoning, it's definitely something worth checking out.
You can either set the DNS on your iPhone or iPod touch by tapping on the blue arrow to the right of your currently-joined WiFi network, tapping on the DNS entry, and typing in the settings, or you can set it on your router and when your iPhone connects to WiFi, it'll pick up the Google DNS settings -- which are the unbelievably simple-to-remember 184.108.40.206 or 220.127.116.11.
For more information, check out the Google Public DNS page.