Re: Got a free Iphone 4 - Now what?
If you're not going to use it as a phone, I'd sell it and buy an iPod touch 4G. (if you want to stay with iOS)
Honestly, iOS is nice in the sense that it's locked down so things don't often crap out on you, but my phone offers more freedom than I could ever obtain on the iPod. iOS is slick and intuitive, but the ability to customize it just isn't there. You're forced to use it how Apple wants you to, which I think is a terrible business model. Jailbreaking does help some with that. (I don't know what I'd do without SBSettings) and the battery life on the Apple devices is usually much better. That's why I use an iPod Touch (my office doesn't get cell service).
As for the app debate, that's a common "iOS IS BETTER" argument, but the truth is, all the apps that matter are on both platforms, and Android has the ability to customize more things (e.g. the keyboard/input method) so there are actually better productivity apps on Android imo. FWIW, I have a Droid X and an iPod Touch 4G.