Just one week after the previous build (15047) we have a brand new Windows 10 Mobile version, build 15051, for all those on the 'fast' Insiders ring - highlights are more bug-fixes, but then we're getting ever closer to a first production build of the Creators Update (Redstone 2). I've had lots of reboots recently and this build should improve things markedly!

From Microsoft:

Today we are excited to be releasing Windows 10 Insider Preview Build 15051 for Mobile to Windows Insiders in the Fast ring.

Other changes, improvements, and fixes for Mobile

• We appreciate several of you sending us feedback on this and last week, we focused on fixing issues that resulted in frequent reboots for some Insiders on Build 15047. If you continue to experience unexpected reboots, be sure to send in feedback to us via Feedback Hub so the team can take a look!
• We fixed an issue resulting in certain inbox apps, such as Calculator, Outlook Mail, Outlook Calendar, Groove Music, no longer being present on the system after a hard reset.
• We fixed an issue resulting in Groove Music not resuming playback after ending a phone call if the app became suspended during the call.
• We fixed an issue where periodically attaching larger photos to a message in Messaging wouldn’t work.
• We fixed an issue from recent flights where, in certain apps, if you had selected editable text and pressed Shift on the keyboard, the keyboard would crash.
• We fixed an issue impacting certain UWP apps using pivots, such as the News app, where the pivot control could end up becoming offset after quickly swiping through the pivots.
• We fixed an issue where asking Cortana to read a text message over Bluetooth with many back to back emoji would result in high pitched distorted noise.
• We fixed an issue where after upgrading some Insiders were unexpectedly seeing the full QWERTY keyboard on the lock screen instead of the pin pad.

Known issues for Mobile

• We have discovered a bug that causes background tasks to not run in the background like they should such as OneDrive’s camera roll sync feature. Please double check your photos have synced to OneDrive on the latest builds. We’ve got a fix for this issue coming in an upcoming build where background tasks will run again and your camera roll will sync to OneDrive as expected.
• If your device experiences an unexpected reboot, in some cases you may lose your call, text, and email history may be lost. We’re actively investigating this issue. If you believe you’ve hit this, please up-vote this feedback item In Feedback Hub.
• Speech packs may be unable to download on this build.
• ADDED: Some users are reporting that pages are constantly reloading or refreshing, especially while they are in the middle of scrolling them in Microsoft Edge. We’re investigating.

As usual, I've emboldened specific issues that have plagued me since last week. There's still work for Microsoft to do though, just read the text above!

How many Fast ring builds will we get before Redstone 2 will finally 'ship' to production phones? My guess is another two, taking us to the last week in March, following which we'll have the official release and then some extra 'Release Preview' builds to tidy final bugs up through April/May.

Which means that at some point soon after the Creators Update hitting, many Fast ring Insiders here might like to consider switching to that (RP) ring, otherwise you'll start to get shunted off into Redstone 3 early builds, and those will be pretty unstable for a while. Just something to think about!

See also my summary of what's new going from Redstone to Redstone 2 (Anniversary Update to Creators Update).

Anyone with an existing phone that's officially deemed Windows 10 Mobile compatible by Microsoft can join in the fun. The full list of phones includes Lumia 430, 435, 532, 535, 540, 635 (1GB RAM version), 640, 640 XL, 730/735, 830, 930, 1520, Icon, BLU Win HD w510u, BLU Win HD LTE x150q, and the MCJ Madosma Q501. Plus, of course, all the devices which have shipped with Windows 10 Mobile in the last year, of which the Lumia 550, 650, 950, 950 XL, Acer Jade Primo, Alcatel IDOL 4S and HP Elite X3 are the highest profile.

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 next year's mobile OS today. Fun, fun, fun....!