Hi, POLIP

Your solution much depends on security and internet media used.

SIEMENS offers following standard solution for SINAUT Micro SC with the MD720-3 GPRS modem:

http://support.automation.siemens.com/WW/view/en/27038105

Also, you may consider secure VPN communications, there are several threads available, one of them is here:

scalance s612 remote and local connection configuration

Personally, I have used ER-75i GPRS/EDGE modem for VPN connections with PG/PC and S7-300 networks

Hope this will help