Join Teams work meetings from Microsoft Teams (free) and vice versa

Microsoft Teams (Free) users can currently join Teams for work (or school) meetings only as guests, which requires them to use a browser and results in a sub-optimal experience. The new feature rolling out will allow these users to join Teams for work (or school) meetings in one click, without being redirected to the browser or asked to fill in their name/surname. They will also be able to continue collaborating with the meeting organizer and other participants via meeting chat after the meeting.  The feature will work in the opposite way as well, so Teams for work (or school) will just as easily be able to join meetings hosted by a Teams Free user with one click. This is associated with Roadmap ID: 167326

How to locate users without the EXT in line uri and add it to them

Sometimes added users do not get their EXT set in their LineURI as they should, and it can be a frustrating to locate these users and to edit the lineURI to the proper format.

Fortunately, we have powershell for those kind of jobs. The following example will locate any csuser with a lineURI but without the extension set. Then add the extension to the lineURI and save the configuration.
$extSet = Get-CsUser -filter {lineuri -notlike "*ext*" -and lineuri -ne $null}
foreach ($user in $extSet){
$myURI = $user.lineuri
$myURI = $myURI + ";ext=" + $myURI.substring($myURI.length - "4") 
set-csUser -Identity $user.displayname -LineUri $myURI -verbose}

The example above will add the extension of 4. Edit this as fit for your environment.
I will add this example to the PsCommands sections as well