Simple, ##786#. Enter your MSL code. Click yes. Phone will format itself (no, not your SD card). It will clear any NV (Non-Volatile) memory. And it will have blanked out IDs for Username and MEID and whatnot. This is not just a factory reset or a /data wipe. After it finally boots up, it will give the 'Hands-Free Activation', followed by 1x connection, followed by 3G.
I am assuming that the ICS update was an OTA, which means that I am unaware of the official Sprint update. I'll read the General forums see if that's what it is. Nonetheless, if this is a custom ROM, be aware that some custom ROMs will NOT properly activate after an RTN reset. In the case that it IS the case; and you don't have any connectivity, even phone services, simply flash a Stock rooted ROM. Edit: I see you did mean the official OTA, so ignore this paragraph as it only applies to a few custom Sense ROMs, and all AOSP ROMs which can accept ##RTN#.
In the case that your phone is not rooted / S-Off, ignore the entirety of the 2nd paragraph.
Hmm, maybe ignore all this, seeing as how I misread it was your WiFi erroring. I do not see how an RTN will fix that. One of the .ko files probably needs replacing.