[viraptor]

I'm having trouble understanding your issue with email addresses. What do you mean by "another service"? What do you mean by "register the phone with gmail"? What do you mean by "sign in with windows live"?

[IkmoIkmo]

I've got no clue, I use the same email account for gmail, microsoft, samsung, facebook etc. I have lots of services with the same email setup.

[philliphaydon]

My gmail is registered as a Windows Live account.

So same email / different password / different service.

I store all my contacts on my Windows Live account.

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When you register the phone with a Google Account it automatically creates an Account for the email associated to the Google Account.

I then want to add a Windows Live account in order to sync my contacts.

Android OS prevents this by disallowing the registration of the Windows Live service by telling me that the email address is already associated with an account.