If you have multiple devices (i.e. iPhone, iPad, iPod Touch), I think you can only use one email per device in the settings. For my iPhone, I setup my @gmail.com and my phone number. For my iPad, I used my @me.com account. The added benefit, I can text myself between devices.
If you're getting the message above, check and make sure you're not already using your primary email as a recipient on one of your other devices.
This is incorrect....the whole point of iMessage is that you can start a conversation using iMessage on your iPhone and continue it on your iPad as long as you are using the same email address on both.
The message about "unable to verify email because it is already in use", means that it is listed as a "verified" email address on *another* Apple ID. (perhaps you entered this email address when you signed up for FaceTime using another Apple ID)....
For example, in my case, my original iTunes accounts (pre-mobileme), is just an account name, i.e.: myitunesacct
If I look at that Apple ID (myitunesacct), one of the verified email addresses is my MobileMe address, i.e.:
mymobileme@me.com
So when I log into iMessage with Apple ID "mymobileme@me.com" and try to use
mymobileme@me.com as an address, it says it's already in use. And it is, it is currently linked to my old Apple ID "myitunesacct".
If you log onto iMessage with Apple ID "myitunesacct" instead, then you will be able to use "mymobileme@me.com" as a verified address.
SUPER confusing, I know.
Supposedly, I should be able to remove the mobile me verified address from the old "myitunesacct", which I did. But it still is giving me the error that it is already in use.....I'm hoping it just takes time to reset and after all the craziness calms down, it will let me use the MobileMe address again.