This is big news, especially for those looking to adopt Windows Phone. According to Microsoft...

The Windows Live team has announced the addition of EASI ID to Hotmail, which allows users to use Hotmail with any existing email address, similar to how email clients like Microsoft Outlook work. Today, most people have more than one email address. With that in mind, we implemented this to give users all the benefits of Hotmail, without the hassle of changing their email address and potentially losing contact with friends from these other accounts. The feature has begun to roll out today, and it will be available to all users worldwide in the next few days. To try it out, users just need to register and validate their email address.

Here's the word from the Windows Live team blog:

We understand. You already have at least one email address and you probably don’t need another. You may also use your existing address for things other than just email, such as signing in to online shopping sites, which makes changing even more challenging. Also, you might have an address that you really like, but a similar name might not be available on another email service. So we looked for a way to make it easier for people to give Hotmail a trial run.

Today we begin rolling out a feature that makes it easy to use Hotmail with any existing email address. Just as you can use Microsoft Outlook with an address from any service, you can now do the same with Hotmail on the web.

To try it out, you just need to register and validate your email address. Over 30 million people have already registered an email address from another service when signing up for a Windows Live ID to use Xbox, Zune, SkyDrive, or Messenger. If you've done the same, then go to www.hotmail.com and sign in with your Windows Live ID. If you don't have a Windows Live ID, you can sign up for a new Hotmail account now and use your own email address when registering.

Hotmail will guide you through connecting to your old service and importing your existing email using POP, and then you can begin sending and receiving mail from Hotmail with your existing address.

As I mentioned earlier, we’re just starting to roll out this change today, so it may take a few days to reach all of our customers worldwide. When it does, please give it a try, and let me know how it’s working for you.