Unlimited 3G Data

I'm on an "unlimited" plan with Verizon, and previously did the same with Sprint. I've tethered my laptop with my Verizon phone on a regular basis - I use it for at least four hours a day while in transit, and I had a dedicated 3G USB connection with my old Sprint account. Both carriers impose a 5 GB "limit" on their unlimited accounts, with the understanding that regular breech of that cap can lead to them restricting your data. Even with my very heavy usage, I never came close to that 5gb limit. I don't think I've ever exceeded 1gb of monthly transfer with a smartphone alone, to be honest.

What are you attempting to transfer over 3G that would require such a large bandwidth allotment? If you must transfer that much while mobile, I'd recommend looking into a 4G connection card or smartphone - I know that neither Verizon nor Sprint imposes any hard limit on their 4G connected devices. Alternatively, maintaining a home internet connection for large file transfers and downloads may save you a bundle - I'm in love with my FIOS connection, although I do miss Comcast+DOCSIS 3.0 at my old apartment. My apartment's connection made FIOS look positively sluggish.

You cannot get unlimited data plans on AT&T. End of. You'll have to switch networks.

You cannot get unlimited 3d, possibly unless you signed up for one before the end of the offering, but that's not your case in your situation