I want to update to the most recent firmware while jailbroken OK so I have the iPhone 3GS (old bootrom) and am currently on iOS 5.1.1. I'd like to update to the most recent firmware WHILE retaining my untethered jailbroken status, Cydia, and the unlocked feature of the phone which allows me to use it without a data plan. 

I've been told to simply update the phone in iTunes - will this retain all the things I mentioned above?

When I click on update iPhone, it says iTunes will "Verify this update with Apple" (or something along those lines) - what does this mean? Does this mean that Apple will know I'm using an iPhone w/o a data plan and will they then notify AT&amp;T?

Lastly, the "backup" that you can create in iTunes is only information - Like, if I tried to back up from a 6.1.3 to a "backup" that was created with a phone on 5.1.1 firmware it would NOT restore the phone to firmware 5.1.1, correct?

Thank you so very much for your time, whoever is able to answer these questions. It means a lot to me. Thank you again, Sebastian
OK, I'll try to answer one-by-one.
Updating without loosing jailbreak
I'm afraid that it's no longer possible. The most recent iOS version - 6.1.3 - does not currently have a jailbreak available. You would keep all you info, but wouldn't keep your jailbreak - nor be able to get it back soon.
Verify this update with Apple
It just means that Apple will sign your update and get stats on what kind of devices are updating, etc. Ever wondered where those percentages they get for the Keynote graphs are coming from? Now you know.
They won't tell AT&amp;T. Even if they did, there is nothing wrong with using a phone without a data plan. Who cares, anyway?
The Backup
Yes, it's only information - apps, app data, settings, pictures, etc.
Restoring to that backup would keep your data and put you on iOS 6.1.3.