So the new 'feature2' builds are still moving on apace for Windows 10 Mobile Fast ring Insider phones (keep up at the back!), with build 15205 now available for 'compatible devices'. And you'll have seen my summarising thoughts on the to-ings and fro-ings over the last week?

From the Windows blog:

Today we are excited to be releasing Windows 10 Insider Preview Build 16179 for PC to Windows Insiders in the Fast ring. We are also releasing Windows 10 Mobile Insider Preview Build 15205 to Insiders in the Fast ring.

Changes, improvements, and fixes for Mobile

• We fixed the targeting issue that caused some variants of the Alcatel IDOL 4S to not receive Build 15204 last week. All variants of the Alcatel IDOL 4S should receive Build 15205.
• FYI: We fixed the issue where supported Windows 10 Mobile devices were showing the update to the Windows 10 Anniversary Update as “not yet available” in the Upgrade Advisor app.
• We fixed an issue where Continuum would stop working when HP Elite X3 case is closed.
• We fixed an issue where Continuum would hang or render incorrectly after disconnecting on devices like the Lumia 950.
• We fixed an issue with Microsoft Edge where you might get into a bad state after opening a new Microsoft Edge windows and screen off with the JIT process suspended.
• We fixed an issue with where the device screen might stay black when disconnecting from a Continuum dock after screen has timed out normally.
• We fixed an issue with backup and restore which impacts users with slower network connection.
• We fixed an issue around Microsoft Edge reliability.

Known issues for Mobile

• A small percentage of devices may experience text message backup loss related to backup and recovery of the messaging database.
• For Insiders who have upgraded from a prior 150xx build to this build, the “Add Bluetooth or other devices” Settings page and the Connect UX page may fail to open.
• The copyright date is incorrect under Settings > System > About. It shows as 2016 when it should be 2017. Thanks to the Windows Insiders that reported this!
• Insiders may experience random shutdowns on some devices.

The Upgrade Advisor entry is a bit misleading - that was nothing whatsoever to do with this build - it was something broken on Microsoft's servers which was blocking any W10M-compatible phone from upgrading to Threshold, the first step to the Anniversary Update. Which they fixed by rebooting or similar. 

So we're now beyond the build of the Creators Update and well into new territory - RS2+, anyone? Who knows, but at least critical fixes and improvements are being made to Windows 10 Mobile 'Fast' ring in parallel to the higher-numbered builds for PC. See my feature on upgrade paths for the various classes of existing W10M handsets.

Anyone with an existing phone that's officially deemed Windows 10 Mobile CU-compatible by Microsoft can join in the fun. In each case:

1. Upgrade to Windows 10 Mobile (if appropriate) using the Upgrade Advisor.
2. After at least one update cycle you should then be on the Anniversary Update (a.k.a. Redstone). Head into Settings/Update & Security/Windows Insider Programme
3. Join the Insiders programme and choose the 'Fast' level in the pick list.
4. Within a few hours your phone should be seeing the build mentioned above and you'll be running the Creators Update and beyond...