Hi,
Dual SIM mobile should have two IMSI numbers, each for a SIM card.
TelephonyInfo telephonyInfo = TelephonyInfo.getInstance(this);
String imsiSIM1 = telephonyInfo.getImsiSIM1();
String imsiSIM2 = telephonyInfo.getImsiSIM2();
You may use the above code to get IMSIs respectively.
Edit 1:
By the way you can get TelephonyInfo.java here
Note: I have not tested the code! I hope it works.
Hope this helps.