Hi Bahrom

The easiest way is to adapt SmsApi

class SmsApi(models.AbstractModel):
	​_inherit = 'sms.api'
   _description = 'my API'

    @api.model
    def _send_sms(self, numbers, message):

        """ Send sms """

        my_api = call the calls of your new provider

        params = {
            'numbers': numbers,
            'message': message,
        }

        my_api.call(make the call)

        return True
# do the same  for _send_sms_batch
	​

   I advise you to create the api calls as a seperate class that you can call

With this approach you ensure that all methods in odoo that calls the sms methods are calling your extension

From versio v17 odoo moved sms.api to a class to be used as 

from odoo.addons.sms.tools.sms_api import SmsApi

this means either you adapt the odoo class or the method using the class SmsApi

Hope this helps