You configured both the Mac and the iPhone to get the mail via pop3, didn't you? If that's so, sorry, that's the way pop3 works, no easy way around it. What I think you could do is automatically forward all your mail from that account to a new one, and configure the phone to get the mail from there (let's call it the iPhone account). You can also configure the iPhone to send mail from the old account (or even configure the iPhone account to send mail with the old account as the return address), so nobody will know about your iPhone account and write you there. If you follow my advise, you might as well get a Yahoo address instead of a Gmail one, so you can get the push mail.