This is going to be something of a short feature, since we're only really talking about one check box in one screen(!), but there are other factors worth commenting on, below.
Most Windows Phones will be set up in similar fashion, with 'Settings/phone update' having the 'Automatically download updates' checkbox ticked. The idea is that, when an OS update is available, the largish update file (often 1GB or more) can be grabbed in the background (over Wi-fi):
The user can then be presented by a 'Update available, tap on 'OK' to install message - as you know, Windows Phone updates aren't speedy at the best of times, so it helps to have the initial large download out of the way, at least.
Happily, this also means that the user (as here, with the 1020) can opt out of the download even happening in the first place. Note that we can't stop Windows Phone 8.1 from 'phoning home' and checking if Windows 10 Mobile is available or not, but at least we can cut the process off before it starts by disallowing the download. I expect that there will still be regular notifications about the availability of W10M that need dismissing (e.g. with a swipe in Action Center), but I can't see why Windows 10 Mobile need to be compulsory. And, on devices with little free internal storage, we've also saved the ignominy of running out of room - or errors - caused by the extra big download.
The exact sequence of notifications is yet to be seen, of course, but with the above box unticked I really can't see why a device couldn't be kept on Windows Phone 8.1 forever.
Which all sounds a bit drastic, except that at this stage there's precisely zero chance of any official update to 8.1 - most devices never even got the Windows Phone 8.1 Update 2, remaining stuck on 'Update 1', because of lack of resources at Microsoft in the middle of 2015. So heading into 2016 and with all 8.1 devices pretty stable there's no chance of an update that's NOT Windows 10 Mobile.
The six million dollar question, of course, is which devices this should apply to. Whether you go for W10M is entirely subjective, but I'm tempted to say any phone with either a S4 processor OR 512MB RAM. And, to save you scurrying for your spec sheet tables, this boils down to:
[table moaners - just rotate your phone to landscape mode to view the whole table!]
|Processor and specs||Update type/date for
Windows 10 Mobile
|Recommended action||Phone models|
|Snapdragon x00 series, 1GB+ RAM||Arriving with it on-board:||n/a||Lumia 550, 650, 950 , 950 XL|
|Snapdragon x00 series (or S4 pro), 1GB+ RAM||Over the air update starting end February 2016 and through April 2016||Update when prompted||Lumia 430, 435, 532, 535, 540, 635 (1GB RAM version), 640, 640 XL, 730/735, 830, 930, 1320, HTC One (M8), 1520, Icon
|Snapdragon S4 or RAM limited||Over the air update
starting April 2016 and thereafter (if ever*)
|Turn off auto-download and defer**||Lumia 520, 525, 620, 625, 630, 635, 720, 820, 920, 925, 1020|
|Snapdragon x00 series, 512MB RAM||Update via PC utility,
starting March 2016
|Turn off auto-download and defer||Lumia 530|
|Various||Likely to stay on
Windows Phone 8.1***
|n/a||HTC 8S, HTC 8X, Samsung ATIV S, Yezz Billy 4, Yezz Billy 4.7|
- * Microsoft claimed, almost a year ago, that the 'majority' of phones would get the Windows 10 upgrade. I suspect that this 'majority' is being whittled down in internal testing and may in fact end up being not much more than 50% - and maybe even less.
- ** at least until you gather more feedback from others who have tried it on the same hardware. I'll do my own share of tests here on AAWP, of course. Just don't jump on day one.
- *** any phones not mentioned (including the odd 'dual SIM' variant) are likely to be from lesser manufacturers and lack of an update is more to do with testing resources.
Comments welcome, of course. I think the table above represents a realistic view of the state of the OS and its requirements, as of the end of February 2016. Even if the likes of the massive-selling Lumia 520 don't end up being offered Windows 10 Mobile, it's really not a big deal in my opinion - such devices are low end, used by teenagers and in other undemanding use cases and these people will probably be very happy staying on Windows Phone 8.1.
The inclusion of the flagships of yesteryear in the 'defer' recommendation, e.g. the Lumia 920 and 1020, may be more controversial, but I can only comment on what I've found so far. The next move's Microsoft's, if it has the will and resources to pull a rabbit out of the hat in terms of W10M and the older processors.