Email-based FaceTime on iPhone 4?
On the iPhone itself, you are unable to add "e-mail address aliases" like in the OSX App. The only method of having people call your iPhone is by giving them your phone number.

As far as the iPhone making facetime calls, the only easy way I've seen to do it is to already have their Facetime address in your Address Book, or use Safari.

Open Safari on your iPhone, go to the URL bar, type: &lt;facetime://their@email.addr&gt;, then tap the "Facetime" acknowledgement button afterwards.