Just a little correction: if they cap you at around 40GB, it's not an unlimited data plan - it's a ~40GB data plan. 'Fair usage' is just a marketing trick so they could call their data plan 'unlimited'.

With that being said, I'd be more than happy to have such a plan on any network in my country. The best you can get here is a combined voice/data plan with 100MB (rounded to 100kb packages) 'free' data (and about 150 mins of voice + 200 SMSes) for about $20/mo, where each subsequent 100kb over that limit would cost you around 12 cents