"Today, we're excited to announce that we've completed upgrading all Hotmail customers to Outlook.com. Coupled with the growing organic excitement for Outlook.com, this has pushed us to over 400 million active Outlook.com accounts, including 125 million that are accessing email, calendar and contacts on a mobile device using Exchange ActiveSync," Microsoft stated in a blog post. "We're also pleased to announce that we're adding two new features to Outlook.com: SMTP send, so it's easier to send mail from different email addresses, and deeper integration with SkyDrive."
Outlook.com was home to 60 million active accounts when it came out of preview in February. At the time, Hotmail was still going strong with 300 million active accounts, leading to what Microsoft deemed an "incredible" and "unprecedented" migration process.
If you're attached to your Hotmail address, you can still use it. Furthermore, Microsoft says you don't even have to change/update any settings on your phone or other apps. And if you're a Hotmail Plus subscriber, your account will continue to work on Outlook.com, Microsoft says.