JavaCard OS

I am trying to write an applet for automatic switch Dual IMSI. But now I still have some question needed to be clarified.
Thanks for any help!
Questions:
1. What is the flow chart for switch IMSI?
2. Is there any specification which will give more details about these issues?

A1:
Roaming is detected when current MCC and MNC is different with Home MCC and MNC, then the applet may decide to switch or not based on the requirement.
A2:
You can check the related specification defined by telco operator!