Magento 1.9 module for sending an sms with the tracking number

We need to create a Magento 1 module which will send an SMS when a tracking number is created in an order shipment. So when we add a tracking number and save the order shipment, the sms will be sent to the customer’s billing address phone number.
Any errors from SMS sending process should be noted on the order comments visible only to admin, and should not prevent the Magento order completion workflow.
For example: Rest service url not accessible, rest service reported an error.

The REST API is this one
https://smscenter.gr/api/docs/en?ModPagespeed=off
Need accurate timeframe and cost

Details of the job:
1. Implement on vanilla 1.9.4.5 instance
2. Make compatible with PHP 5.6 and 7.2 for transitioning step.
3. We install on staging site and report compatbility issues
4. Fix compatibility issues.
5. Test and move to production.