There are a number of ways to add activities to a contact's timeline. If you're looking to create notes, you'll want to check out the Engagements API. The Engagements API also allows you to create timeline activities like meetings, emails, calls, etc.
hi @Derek_Gervais Need your help I have to store sms activities in hubspot But Engagements api don't support SMS type Engagements only supports - NOTE,Call ,email,task,meeting