Calling method, device, and system

A service platform, comprising:

• a subscription information modifying unit configured to obtain subscription information from a roaming prepaid subscriber and modify the subscription information;
• a subscription information sending unit configured to send the modified subscription information to a Visited Mobile Switching Centre (VMSC) of the roaming prepaid subscriber so that a call initiated by the roaming prepaid subscriber could be triggered to a call receiving unit by the VMSC;
• the call receiving unit configured to receive the call to a called subscriber initiated by the roaming prepaid subscriber and triggered by the VMSC;
• a callback service determining unit configured to determine from the call that the pre-paid roaming subscriber has activated a callback service;
• and
• a call processing unit configured to instruct the VMSC to release the call initiated by the roaming prepaid subscriber and instruct a call connection device to connect the roaming prepaid subscriber to the called subscriber, after determining that the roaming prepaid subscriber has activated a callback service.

A calling system, comprising:

• a service platform configured to:
• obtain subscription information of a roaming prepaid subscriber, modify the subscription information, send the modified subscription information to a visited mobile switching centre (VMSC) of the roaming prepaid subscriber so that a call initiated by the roaming prepaid subscriber could be triggered to the service platform by the VMSC,
• receive the call to a called subscriber initiated by the roaming prepaid subscriber and triggered by the VMSC, and instruct the VMSC to release the call initiated by the roaming prepaid subscriber, and
• instruct a call connection device to connect the roaming prepaid subscriber to the called subscriber after determining that the roaming prepaid subscriber has activated a callback service;
• a visited mobile switching centre (VMSC) of the roaming prepaid subscriber configured to:
• receive a call initiated by the roaming prepaid subscriber,
• trigger the call to the service platform according to the subscription information of the roaming prepaid subscriber, and
• release the call according to an instruction received from the service platform.