You can already do this! If you want to call a mobile phone or any number from Teams, just click the little phone labeled “Calls” then click the button that says “Dial a number.”
Note this is only available for certain licenses such as E3 with enterprise voice add-on and E5. You also need to have been given a calling plan by your administrator.
Please let me know if you have any questions.
Nowadays Hospital industries are also shifting towards VoIP technologies and using the virtual based number for communication purpose. Check out this for more info- https://callhippo.com/solutions/industry/healthcare-phone-solution
There is no requirement of phone system licenses at https://callhippo.com/enterprise-level-hosted-phone-system]CallHippo. You can easily use CallHippo's services in less than 3 minutes.