If and when VZW gets around to it. You'll get no official word here on the community and have a better shot hearing about if on tech sites then here.
If you want the update now, install the Windows Insider Preview app and select the fast ring. Once Windows 10 Mobile is installed (and do a hard reset after installing and, a must. Do not restore a backup either) opt out of the preview program. My Icon is running well on the latest release.
There's no firmware updates for the Lumia's at this time.
Windows 10 Mobile on VZW might be looking slim. After Microsoft successfully pushed out an update to the 550, 950 (XL) with out the carriers approval might not sit well with VZW. VZW likes to control this to a certain point.
Microsoft new strategy is that they removed the radio stack from the OS. In doing so they can push updates technically without carrier's approval being there is nothing in the updates that will ever touch the radio stack. If there are changes to the radio stack then of course the carrier will have to test and approve before being pushed out.
If VZW doesn't like this new approach; and most likely they won't, we might not see Windows 10 Mobile being pushed out by the VZW unless the force Microsoft not to directly push OS updates to go through VZW for approval first.
We'll have to wait till Microsoft pulls the trigger and starts updating Windows Phone 8.1 devices in the next few months.
Hmmm. Verizon accepts this updating from Apple on the iPhone, so it's not like they've never done it before. But then I guess the iPhone is a phenomenon, and after two years of missing out on it while AT&T had the exclusive, I suppose Verizon will take more dictatorial terms from Apple than from others.
That's a nice thing about iPhones - no carrier bloatware. Also updates from Cupertino and not Verizon.
Verizon is involved with the update from Apple. They all do the ADC which is required if you sell the iPhone. Also Apple doesn't push updates is all finished and not in different times giving the illusion it's timely.
You can get Win 10 now on the Lumia 735 (I am running it now and have been for 2 weeks) using Windows Insider, either slow or fast ring.
Seems to work well
I have a 2nd 735 which is not on Windows Insider and expect it have the upgrade available at some point in the future.