Most of the buzz around Windows 10 has centered on its desktop incarnation, but Windows 10 offers plenty of excellent new features for smartphones, too. Sure, the desktop version brings Cortana, windowed modern apps, and the Action Center, but smartphone users will benefit greatly from improvements specific to mobile usage, including new swipe-down Action Center options, interactive notifications, a new Photos app, and the ability to use voice input any time the keyboard appears, just for starters.
The biggest new idea for this phone operating system ,however, is that it will be integrated with Microsoft's desktop operating system, running the same apps, syncing settings, using the same browser, and actually sharing the same underlying OS core. It's pretty ambitious to meld phone and desktop operating systems, especially when you consider that Microsoft is appeasing longtime Windows users by reverting some things on the desktop, such as the Start Menu.
Getting Windows 10 for Phones
First come the warnings: The Technical Preview of Windows 10 for Phones is probably the earliest in the development cycle Microsoft has ever offered. That, of course, means you should expect glitches, lack of functionality, and lack of polish. Most people probably shouldn't install this software, and definitely not for a primary or an essential phone.
But if your curiosity about new mobile operating systems is simply unquenchable, you can get the preview and install it on your Windows phone. Most carriers are supported, and more models will be added as new previews are released. The build is available in 25 languages, though not all interface elements have been translated. Luckily (and uncharacteristically for beta Microsoft operating systems), there's a rollback capability if you want to restore the phone to a stable OS version.
Step 1: Join the Windows Insider Program. Point your browser to the Windows Insider Program. You'll have to sign into a Microsoft account. The page comes with warnings that the program is just for those with some tech savvy. It also explains that the point of this exercise is to give Microsoft feedback data to help it build a better OS. To that end, you're encouraged to visit the Insider Hub and forum, but that seems targeted at desktop testers, as there's no Insider Hub app for phones yet.
Step 2: Choose Phone. Once you're with the Program, you'll get to the page where you can choose whether you're interested in Windows 10 for PCs or for phones. Obviously, we'll choose the latter for this exercise. Once you click Phone, you'll be treated to more warnings about how unfinished the OS is and that it's just for experts. From here you can also see the all-important information that the installation only works on a limited number of phones: Lumia 630, 635, 636, 638, 730, and 830. Microsoft's Gabe Aul has stated that the next update of the prerelease software will include more phone models, and that the updates will come along roughly once a month, so that should change soon.
There's also information on features not available in the prerelease build: dual-SIM support, search, message drafts, sharing voice notes and ringtones, Bi-Di language support, international assisted dialing, spam filter, viewing all group recipients, reminders and quiet hours through Cortana, Rooms, multiple attachments, and GSM support.
Step 3: Download and Install the Windows Insider App. Tapping Get the Preview button shunts you to a final warning page that links to the Windows Apps+Games store page for the Windows Insider app. You can install it onto your phone remotely right from this page (a cool capability shared by Android but not by iOS).
Step 4: The Windows Insider App: Choose Fast or Slow. Run the Windows Insider app and log in to the same Microsoft account you did in the previous setup. After you do this, you'll next tap Get Preview Builds, and then have a choice between Insider Slow and Insider Fast. As you may guess, choosing the former gets you new builds later but they're more likely to be stable. If you choose Insider Fast, you'll see new features sooner, but you're more likely to be left in the lurch if a bug shows up.
Step 5: Install Windows 10 on Your Phone! Once you've made that choice, the phone will reboot, and a phone update will be available to install to take you to Windows 10. Be prepared for a very long installation process with reboots. On my test Lumia 830 , the whole process (I of course chose Insider Fast) took 3 hours and 46 minutes, with long download sessions and a couple of reboots along the way. Do note that the Wi-Fi connection used for this process wasn't the fastest around, so you may finish faster. Others have reported install times as short as 45 minutes.
After this, you're done, and you can start enjoying the fantastic new features of Windows 10 on your phone. Despite all of Microsoft's grave warnings, I haven't encountered any show-stopping crashes while using the preview OS.
For a walkthrough of what's new in the operating system, real our Hands On: Windows 10 Technical Preview for Phones. You can also check out our favorite Windows 10 Universal Apps (they actually work in Windows 8.1, too.) For the installation process for Windows 10 on the desktop, read How to Get and Install Windows 10.