People with knowledge of the matter have hinted that Windows 10 Mobile could launch as soon as today, and now there’s more evidence that this is indeed very likely to happen.



The latest confirmation comes from T-Mobile Croatia, one of the carriers that are gearing up for the release of Windows 10 Mobile. It thus confirms that Microsoft is indeed very close to giving the go-ahead to the operating system for a number of devices.
This is actually the most important bit of information, as not all Windows Phone models would get Windows 10 Mobile as part of the original wave. The plan is to bring the new OS on absolutely all handsets running Windows Phone, but for the moment, the staged rollout will include only a handful of models.
Models getting the upgrade in the first wave T-Mobile Croatia says the following models will be upgraded to Windows 10 Mobile in the original rollout that kicks off today:

Lumia 435 single- and dual-SIM

Lumia 535 single- and dual-SIM

Lumia 635 1GB

Lumia 640

Lumia 640XL

Lumia 735

Lumia 830

Lumia 930

Lumia 1520

Microsoft has also provided its very own list of devices that’ll be upgraded to Windows 10 Mobile as part of this first wave, and the big difference
is that Lumia 1520 is included in T-Mobile’s version whereas the flagship is nowhere to be found in Microsoft’s.

The super-popular Lumia 520 doesn’t seem to be mentioned in either of the lists, so it’s pretty clear that this model will be left behind at first. A second wave, however, is supposed to expand Windows 10 Mobile's availability to the rest of models running Windows Phone, so Lumia 520 could get it too at some point in the future.
Microsoft’s official announcement coming later today should set things clear in this saga and provide us with all the information we need on the release of the new operating system.