HTC Sensation 4G owners were thrilled to find out that their Ice Cream Sandwich update was finally coming from T-Mobile this week – tomorrow, in fact. But PCMag spotted a frustrating caveat in the official support document: you won’t be able to use the “4G Hotspot” function for free anymore. Users who wish to share their connection will have to fork over $14.95 a month for the official tethering plan, allowing them to “officially” use the WiFi hotspot or USB data tether.

T-Mobile’s new stance echoes the one taken by all four of the major US carriers, who charge extra for tethering and attempt to dissuade users who opt for alternative (free) services. AT&T goes as far as automatically signing its customers up for a tethering plan if they detect unauthorized usage. T-Mobile has technically had its Hotspot plan in effect for over a year, but has not actively monitored its users to see if those who weren’t paying were using the service anyway. T-Mobile still has technically unlimited data plans, but speeds are capped after a certain amount of bandwidth is used by a single customer.

T-Mobile claims that its somewhat lax enforcement of its own pricing policy was due to a limitation of the software at the time. With the upgrade to Ice Cream Sandwich, they’ll be actively monitoring connections to see if those who haven’t paid for hotspots and tethering are using them. A few short connections probably won’t trigger anything, but sustained and regular tethering use almost certainly will. Instead of automatically signing up customers a la AT&T, they’ll simply deny Internet access to anything beyond the device itself.

The update for the Amaze 4G doesn’t say anything about tethering, but it’s safe to assume that the same policy will be in place once the upgrade rolls out. It’s still unclear whether non-standard tethering methods, popular with rooted users and those with custom ROMs, will be monitored as well.

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