ST18a updated this afternoon to the second release of ICS (was using first release previous to this).
USB Tethering and Wi-Fi Hotspot are no longer working. I can connect and get an IP address but no internet access.
This is real bad since this is a primary use for my phone.
UPDATE: Confirmed same behavior with a second laptop ... I can connect to the Wi-Fi hotspot on my phone but no internet access.
UPDATE: iPad via Wi-Fi Hotspot, same thing, gets IP address but no internet access.
Bob H
Hello friends,
I had upgraded my Xperia Pro (MK16i) to ICS before a week and wasn't having any significant problems with it until I tried to access my phone's data package via my laptop through wifi tethering. I experienced the same problem stated in this thread. I could surf using the data package through my phone. But while using wifi tethering my two laptops and other phones could connect to the wifi of the phone but there was no data transfer.
After reading few comments on this thread and doing some research on the internet I found a solution to this problem.
When I was using GB my phone was having three Access Point Names (APNs) of different types viz. internet, wap and mms. But after upgrading to ICS my carrier sent me only two APN profiles (wap & mms). I read a suggestion on this thread which stated that I should edit my APN type from "wap" to "internet" but unfortunately that didn't work for me at all.
I searched on google for the correct internet type APN settings for my carrier and created a new APN manually.
Settings --> Wireless & networks --> More --> Mobile networks --> Access Point Names --> Menu Key --> New APN
Voila! It worked! 
My wifi tethering started working with the internet type APN and I was able to access internet from my laptop connected to the phone through wifi tethering.
Also my internet speed is better on internet rather than wap type APN (which is just my own experience).
Please note that settings for my internet type APN profile were quite different than wap type APN so just changing the APN type won't work (might work on some carriers but it didn't work for me). Also my phone wasn't connecting to the network at all when I was entering incorrect internet type APN settings.
I found my carrier settings on the following page:
http://forum.xda-developers.com/showthread.php?t=564459
If you can't find the correct internet type APN settings on this page or google, you can request your operator to provide you with the same.
Make sure the internet type APN is working on the phone first before trying to connect through wifi tethering.
This is how I solved my broken wifi tethering problem, I don't know if it will work for all. Try it out and let us know.
0online
1870792posts