Is there a way for me to send sms using the vapi phone number? if so how because there is a way to send SMS using the sms tool but not via api? so how does the Sms tool does it? and can we replicate?

Yes, import a Twilio number, enabling the built-in sms tool in your assistant, and triggering it through flows or the API, this can be replicated using vapi API and webhooks for automation..