The Retarus SMS for Applications REST API is a service to send SMS and lookup the status.
To obtain a test account for this service or any of our other SMS services, please contact Retarus.
https://developers.retarus.com/_mock/sms/sms4a-api/
https://sms4a.de2.retarus.com/rest/v1/
https://sms4a.de1.retarus.com/rest/v1/
https://sms4a.eu.retarus.com/rest/v1/