"Why Teams..."
Simply because it offers significant additional features:
It gives users not only the ability to have group video chats, but also the ability to do free one to one calls/text to friends and colleagues when they are available just like an ordinary telephone phone from the desktop or mobile device in a single integrated app etc.
This together with the wider Teams community groups provides an integrated set of options to communicate and get involved as well as maximising your time and minimising the effort that is required.
Your Personal Phone system...
Teams
Personal Contacts Lookup
You can create a personal 'contacts' list of friends that are also on Teams and do an audio (or video) call anytime to chat/Text with them for free. (Desktop & Mobile) all integrated into the single application.
You can invite others into any ongoing call anytime if required, as well as check on their availability status etc.
As well as this 'one to one' calling phone system you can setup common interest 'groups' of individuals and schedule regular meeting with the same friends. (e.g. an Group call)
You can also dial standard external PSTN numbers for inclusion(not free) with the call or include non Teams users can be sent invites to join a call via browser etc.
It is possible to also purchase 'stand-alone' desk style phones which have Teams built in (and certified) but these are not cheap.
A low cost option can be accomplished using an existing VOIP phone which has Bluetooth to link up with say your mobile phone (which has the Teams app) and hence answer/dial call through that handset connection of your VOIP desk phone.
