Use MobileMe push email with any email address

You can set up MobileMe to use any email address as a 'push' email on the iPhone. The first thing you need to do is set your non-MobileMe (.Mac) email address for auto-forward to your MobileMe (.Mac) account. 

When you create the email account, make sure you set it up as Other (not as a .Mac or MobileMe account.) Then select IMAP as the type of account. Enter the name and auto-forwarded email address. (This is the email address that will show as the "From" email, even though you're using your MobileMe account.) 

For your mail server settings, use your MobileMe settings: 
Incoming settings: 

Host Name: mail.mac.com
User Name: MobileMe user name
Password: MobileMe password
Outgoing Settings: 
Host Name: smtp.mac.com
User Name: MobileMe user name
Password: MobileMe password
Advanced: 

Use SSL - On
Authentication - Password
Server Port - 587

Now you're able to receive 'push' email from your non-MobileMe account, and reply without using the @me.com address. (You can use those same settings in the Mail App as well.)