A reader has sent us a little tip that MobileMe email aliases are now supported in iPhone OS 4. Apple describes MobileMe email aliases as "nicknames" for your account. When you join MobileMe you have a primary user name/email address, but Apple also allows you to create five "nickname" aliases that you can send and receive email with. The advantage of this is that if you go to a site that requires you to register your email address to log in, but you're worried about getting spammed, you can create an email alias in MobileMe and use that new email alias as your email address.
All emails sent to that alias show up in your primary account's inbox. If you suddenly start getting spammed, you can just delete the email alias and any emails sent to that old alias will not make it to your inbox. Aliases are also good for shopping sites or using as separate personal and professional email addresses.
Since Apple introduced email aliases in MobileMe, you could always use them to send and receive email, but it had to be done in the Mac's desktop Mail client or on MobileMe's webmail site. It looks like you will also be able to send and receive emails from your MobileMe email addresses using the Mail app in iPhone OS 4.