The PASA service is a free service provided by Benjamin Ansbach. It allows you to obtain a free PASA account at no cost.
Your phone number will be saved (hashed) on the server after the PASA is distributed successfully. If the verification fails for whatever reason, it will be deleted after 1 hour.
It uses twilio as a SMS service provider. For more info on this service please see the twilio homepage.
The source code of this service is open sourced and accessible here.