Windows 10 has been released for the following devices in March 2016:
- Lumia 1520
- Lumia 930
- Lumia 830
- Lumia 730/735
- Lumia 640/640 XL
- Lumia 635/636/638 (1 GB)
- Lumia 540
- Lumia 535/532
- Lumia 430/435
- BLU Win HD w510u and Win HD LTE x150q
- MCJ Madosma Q501
To get started, you'll need to download the Windows 10 Upgrade Advisor app. Note that actual availability of the update for your phone is dependent on carrier approval.
For more information, see the following links:
As for other phone models, according to this AAWP article, it's seeming more and more likely that anything from the Lumia x20 series (520, 920 and so on), as well as phones with less than 1 GB of RAM, will not be able to upgrade to Windows 10 Mobile. Hopefully Microsoft will clarify the situation with these phones soon.
As for the best channel of information, Windows 10 is such a big deal that every major news outlet, tech-related or not, will report on any significant milestones as soon as information becomes available. You'd really have to go out of your way to remain in the dark. That said, a couple of good sources to keep an eye on:
- Blogging Windows
- Windows Central
- All About Windows Phone
- Thurrott.com
- Neowin