It seems many people having issues with WiFi in 4.0 builds when SIM-Card is inserted.
WiFix tries to solve this problem by changing the WiFi country code.
Using WiFix Manager you can easily install/update WiFix.
NOTE: Make sure to dial *#94349# (*#WIFIX#) after installing WiFix.
Visit http://www.fardjad.com/android/wifix/ for more info.
WiFix and WiFix Manager are licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. Visit http://creativecommons.org/licenses/by-nc-nd/3.0/ for more information.
1/25/12 WiFix V1.1, WiFix Manager V1.2:
Changed minimum SDK version and API Level to 3
Minor layout changes
Minor bug fixes
1/30/12 WiFix V1.2, WiFix Manager V1.3:
Added custom country code support
7/3/12 WiFix V1.2, WiFix Manager V1.31:
Minor layout bug fixes
Compiled with Android SDK 14
12/9/12 WiFix V1.2 WiFix Manager V1.32:
Minor bug fixes (Device compatibility improvement.)
Added reboot prompt after installation and removal.
Compiled with Android SDK 16