Hey Tytung thanks a lot, I flashed your wifi calling zip (WiFi-Calling-htcleo-ICS_for_NAND_v2.zip) and GanOptimizer.apk_update.zip and now wifi calling works flawlessly on your ICS v2.3 ROM. That was the problem, wifi was disconnecting when the screen was off. I also set wifi to never turn off.
So basically to get Wifi calling working on ICS, at least on Tytung's ICS NexusHD v2.3 ROM, this needs to be done:
1) Flash the Zip file that sets the Wifi to high performance:
http://xdaforums.com/attachment.php?attachmentid=1148238&d=1340388909
2) Set the Wifi to never sleep (System Settings>Wifi hit menu go to the Advanced Menu, Set "Keep Wi-Fi on during sleep" to "Always")
3) Flash the latest Wifi calling zip file (WiFi-Calling-htcleo-ICS_for_NAND_v2.zip, from June 18th)
Wifi calling works great, much better than with gingerbread in my experience.
Sent from my NexusHD2 using xda premium