If you have already integrated the 4 software together so that you use Aircall for telephony, Sakari for SMS and MMS and that everything is logged in HubSpot.
1-Buy a phone number in Twilio
2-Add the phone number in Sakari
3-Add the phone number to a group in Sakari to limit who can use this number
https://support.sakari.io/hc/en-us/articles/360039259551-Create-Phone-Number-User-Groups
Note: If it is a user's number that will be used to send automated SMS from Hubspot Workflows, you also need to add a tag to the group in the right way: https://support.sakari.io/hc/en-us/articles/360038865052-HubSpot-Run-As-Workflow-Field
4-Add the number to Aircall
Step 1: https://help.aircall.io/en/articles/3819515-sip-trunking-using-your-twilio-numbers-with-aircall#:~:text=Add%20Your%20Twilio,your%20Twilio%20number.
Step 2: https://help.aircall.io/en/articles/3819515-sip-trunking-using-your-twilio-numbers-with-aircall#:~:text=Send%20Aircall%20Your,trunked%20number.
5-Configure the number in Aircall
https://help.aircall.io/en/articles/5664430-setting-up-your-aircall-number
6-Add the number in your HubSpot integration with Aircall
Step 1: https://dashboard.aircall.io/integrations/hub/hubspot/50218/general
Step 2: https://dashboard.aircall.io/integrations/hub/hubspot_operations_hub/50372