If this is not their phone, made by them, how can they brick them? How is that legal?
That's the point of the GPL. If the users took care of only buying products including only GPL'ed software, then they would have the freedoms: 1- to use the software, 2- to copy it for their friends, 3- to get the source to audit it and modify it (so they would be free to remove any backdoor that wouldn't exist in the first place for this very reason), 4- to compile the source to binaries and use them to replace the provided binaries (so their may increase their level of trust of the software they run on their hardware).
Do not buy products that come with freedom-restricted software!
Even if there were an alternative OS, I'd say it's still pretty well bricked, since installing alternative OSes is outside the skill level and/or comfort zone of most consumers.
I mean, I recall discussions of whether something was really bricked if you could rescue it by hooking up to a JTAG header.
Practically every device i've ran into that has been bricked has been put into that state via software. It may be impossible to fix such state without a JTAG bus and code from the manufacturer, or by desoldering chips, but I can't remember recently when something bricked was truly destroyed and every recovery method was rendered impossible.
(bearing in mind I wouldn't consider something like a ran-over laptop to be 'bricked', but rather just destroyed)
I'm sure some folks use the term when they are referring to destroyed equipment (a 'bricked' gpu from overheating) but I haven't really encountered it personally.
Whenever I get an update on iOS you get the lovely huge Apple T&Cs, which you have to accept to install the update.
So if SilentCircle does the equivalent and put in there "in the event that this is running on a non-approved device, we'll disable the software" then I click "I agree" it would seem fair enough for them to so.
If I were them I think playing it a little cooler would've been to pop-up "Hey this is a knock-off device, we're not letting you use all the cloud service and you're getting no updates from us" and leave it at that...
From the screenshot, it's not entirely clear to me that the baseband is actually bricked. The updated OS refusing to run on some phones isn't the same as damaging the phone.