In the broader context of sending SMS with Java, can Twilio be used to send messages from the same phone number as is on the SIM chip on a physical phone?
Something along the lines of https://sms.ilpostino.com.ar/ in SMS functionality, where there's a corresponding app so that the phone itself is used as a gateway.
Twilio seems to be strictly an API.
No, this is not possible. If you wish to use the number that was previous "on" your SIM card, you can request to port this number to Twilio.
While it's possible to make calls from verified numbers, it's not possible to send SMS from these sender IDs.