When subscribers are abroad in roaming they seek for cheaper calls. This is where Callback application come into place. The Callback applet is a SIM Card based Java applet, which helps the home MNO to trigger calls from the server side automatically or by manual triggering using cheaper networks, every time a subscriber is in roaming and wants to place a call to a counter party.
The Card Centric Callback applet uses the standard Javacard framework, which means it will be interoperable on any Java Card supporting the Javacard Sim API.
Callback Application Specifications
4KB - 5KB
Java 2.1.1 or higher
SIM based applet (independent or built in STK)
For all SIM/USIM cards Service 28- Call Control shall be active.For USIM cards Service 30- Call Control by USIM shall be active.
Independent of SIM Vendor