Among US national carriers, T-Mobile has been the most lax in enforcing the charge for its smartphone hotspot plan, a $14.99 surcharge it first started offering in late 2010 — some phones could simply use the feature out of the box whether you'd paid for the service or not. That's changing, though, brought to light most recently by the Sensation 4G's upcoming Android 4.0 update, which points out in its changelog that users "will be required to add Wi-Fi Mobile Hotspot feature in order to use the service" after the phone is upgraded. T-Mobile blames the free ride on "technical limitations" in software, and while it has the capability to detect hotspot users remotely (as most carriers do), the detection mechanism isn't always quick or reliable. PCMag points out that users of other T-Mobile devices — the Amaze 4G, for instance — have already been dealing with an effective hotspot lock pre-Android 4.0, but for Sensation users accustomed to free tethering, this week's ICS update comes at a price.