What would happen if I jailbreak my Iphone 6s that is on a contract with T-Mobile?

What would happen if I jailbreak my Iphone 6s that is on a contract with T-Mobile? - 1

You would have to hope nothing goes wrong with it, and you may need to be wary about upgrading the OS. You have agreed a license for the use of the equipment so in theory they could sue you (but this only applies to tablets, not phones so you are OK) but in practice they are more likely to refuse to honor any warranty. If they ended up with a test case it is almost certainly likely to find in favor of the consumer. One real risk is that you are far more susceptible to virus attacks.

You will be able to install 3rd party apps and tweaks.

Jailbreaking is against Apple's terms of service and also T-Mobile's terms of service, meaning if anything goes wrong with your device while jailbroken and you can't fix it, then they are in their right to not help you either due to a breach of contract. Nothing else will happen though, there's no way of them finding out if you're jailbroken and even if they do find out, they won't do anything about it as it isn't a legal issue

Other than getting a lot more control over the device, nothing.

Just don't expect any help from Apple or your carrier if anything goes wrong.

The FBI would have access to your phone and all your secrets. It could use the camera and microphone to hear and see you all the time.

You go to jail

Well you probably can't right now unless your running 9.1