Callback Application
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.
![](http://www.cardcentric.net/wp-content/uploads/2021/01/call_back_watermark.jpg)
Callback Application Specifications
![](http://www.cardcentric.net/wp-content/uploads/2021/01/imei_tracker_app_size.png)
Application Size
4KB - 5KB
![](http://www.cardcentric.net/wp-content/uploads/2021/01/imei_tracker_java.png)
Technology
Java 2.1.1 or Higher
![](http://www.cardcentric.net/wp-content/uploads/2021/01/imei_tracker_sim_appket.png)
Architecture
SIM Based Applet (independent or built in STK)
![](http://www.cardcentric.net/wp-content/uploads/2021/01/callback_file_system.png)
File System
For all SIM/USIM cards Service 28 - Call Control shall be active. For USIM cards Service 30 - Call Control by USIM shall be active.
![](http://www.cardcentric.net/wp-content/uploads/2021/01/imei_tracker_sim_vendor.png)
SIM Vendor
Independent of SIM Vendor