It has been confirmed that AT&T will be the first US carrier to sell a Samsung Galaxy S4 with a locked bootloader. We would have expected this from Verizon, but AT&T devices have been pretty open in the past. Samsung has been developer friendly with the exception of Verizon devices. This could signify that other carriers are forcing the hand of OEMs to lock up devices. AT&T will be authenticating recovery and boot images before executing them like Verizon. Not only will this make things more difficult for consumers who wish to tinker with there phones, but it could cause updates to come at a much slower pace as we have already seen on Verizon.
Steve Kondik of Cyanogen gave the confirmation yesterday. He had this to say.
The only way to combat this sort of behavior by the carriers is to vote with your wallet. It is a good thing that the option to buy an international unlocked variant is available for AT&T customers. Verizon users have had options to purchase developer variants from Motorola and HTC. Hopefully OEMs will continue to give us these kinds of options in the future.Yep, it's confirmed. The AT&T S4 authenticates the recovery and boot images before executing them.
I can't see what AT&T has to possibly gain from this. GSM and LTE aren't magical, tethering is controllable on the server side, and theft-of-services is not possible from the application processor side (or even from the modem side as far as I know). The same device is available on every carrier, so it's not an exclusivity issue either. The modem processor has always been locked, and the casual user doesn't want to mess with that part anyway. Samsung has always been developer-friendly, so I am guessing their hand was forced.
The only outcome I see here is stacks of bricked devices being sent back for warranty replacement due to the ease of causing a permanent boot failure, especially since the device is trivially rootable.
The arms race continues. News flash: MILLIONS of people run custom firmware (and I have the STATS to prove it). This is just a stupid move that will cost you customers and money.
I would not recommend buying this device on AT&T if you want to run CyanogenMod or another custom ROM, or if you are a developer and need to work with or debug the lower layers.