Can mobile carriers detect if you jailbreak a bill pay iPhone 4s?

I'm thinking about jailbreaking my iPhone but have not been able to find out anything on this question. Can carriers detect if you jailbreak your iPhone? I'm on bill pay with eMobile and I'm wondering if they will charge extra money/cancel the contract/take the iPhone back/refuse to fix it if I jailbreak the device. All answers are appreciated

No they can't detect it, they personaly probably do it too!

There's no reason forn them to take it back!