Windows 10 may arrive earlier than expected. Previous info had us marking July,29th on our calendars, but Microsoft is testing candidate builds for both computers and phones. Now, Microsoft may go through a number of candidates before ironing out all issues, but the builds currently in testing reportedly look promising.
They are undergoing the review process and a decision should be made soon. There was an impression that Windows 10 Mobile, the smartphone version, will launch later than its computer twin, but now it sounds like both versions are going hand in hand.
The Mobile version has been available as a Technical Preview since mid-February. Since then it has become clear that all WP8-running Lumia phones (and non-Lumia ones) will get Windows 10 though those with 512MB RAM will have some limitations.