If I jailbreak my iphone 4s?

Under Att contract now will I still have service with att right after the jailbreak or is my Att service stopped?

You will still have service but as seeing you asked this question i'd have someone that knows what they're doing to jailbreak it for you because you can mess up your phone if you don't have a clue what you're doing.

It won't affect your service at all.

Backup to iTunes before you jailbreak. If you don't like the jailbreak and want to go back, restore your iPhone to that backup.

EDIT: I agree with the other guy. If you're asking a question that basic, I don't think jailbreaking is for you. You need to know what you're doing or you'll mess it up.

Jailbreak will not affect your service.