The long-awaited update to Ice Cream Sandwich often brings a few teething troubles with it, and such is the case with T-Mobile's HTC Sensation 4G. After the scheduled Android 4.0 update yesterday, some users found that their HSPA+ ("4G") data wasn't working, much to their display. Luckily, TmoNews discovered an easy work-around: head into the settings menu, tap "Network", then switch it to WCDMA/GSM Auto. You should see the little "4G" icon reappear when in a coverage area.
T-Mobile should fix the issue the next time they have a maintenance update. Of course, a slight interruption in wireless service isn't the only troubling thing about the Sensation ICS update: T-Mobile is also ending its grace period when it comes to "unauthorized" tethering. Rooted users who skirt around T-Mobile's official, paid tethering solution will be blocked if detected after upgrading their phones.
The only other phone on T-Mobile that's confirmed to get an Ice Cream Sandwich update is the HTC Amaze 4G, which may have similar issues on both counts. (Samsung says they'll update the Galaxy S III and Galaxy S Blaze 4G, but T-Mobile's been silent thus far.) Of course for both phones there's plenty of custom ROM options, if you're not particularly attached to your warranty.