1) connect GSM-gateway Polygator to Ethernet
2) insert SIM-cards
3) in special file specify your server address and data format (i.e. POST/JSON)
Since that moment, each incoming SMS sent to your server as a JSON-object,which includes message text, sender number, SIM-number etc. The same way GSM-gateway may pass incoming calls information.
Of course, this solution may be improved. For example, by using Remote SIM-Management technology. You may have small GSM-gateway and hundreds of SIM-cards in reserve (in SIM-bank). It is possible to put SIM-cards into GSM-network either by queue or by API-command etc.
The solution may be helpful for receiving one-time passwords (OTP) and confirmation codes when activating accounts in various online services, social networks etc.