Some users of the Google Galaxy Nexus have been reporting connection issues after updating to Android 4.0.4 Ice Cream Sandwich. The update reportedly causes some devices to loose their cellular signal when left in standby mode for a couple of minutes.This means that you cant receive calls or text messages nor establish a data connection. The connection is restored once the device is brought out of stand by, but you may have missed something important by then.
Users who have tested this issue have reported that the problem doesn’t occur when there is a background application which puts a load on the processor. It has also been found that the problem disappears when you downgrade to Android 4.0.2.Fortunately this issue only affects a few Galaxy Nexus (GSM) devices. Google is reported to have been made aware of this issue and any users who are affected by this issue can be sure that a fix should be on the way soon.
If you are facing this issue on your device please let us know in the comments section which follows.
source - Google | XDA Developers