To receive the update, users will have to tether their handsets because Sony wants users to make a "conscious and informed decision to upgrade".
There is a problem with these updates though, is that none of them will be over-the-air (OTA), and will require that owners of these handsets who want to upgrade have to tether their handsets.In a post on Sony's Mobile blog, the firm warns that Ice Cream Sandwich is more resource intensive and may slow down your phone.
This is because Sony wants users to make a "conscious and informed decision to upgrade". All this means is that while Sony are pushing out ICS updates for 11 handsets, those who don't know about ICS will have to wait until Sony push them OTA, if they even bother doing so. I would expect a notification from Sony saying "your phone is compatible for an update, if you would like to do so, visit this site", and that site explains what ICS is, and how you upgrade.
Source: TweakTown