I had a grandfathered unlimited data plan with AT&T until May. It was a 21 year old account. If you’re in a metropolitan area, I recommend you take a look at Sprint - they spent a huge chink of their holdings in just the last couple years upgrading their 4G network and I have zero complaints about switching. They have an iPhone Forever plan that might be worth looking into.
I’m an Android girl and walked out of a Best Buy last May with a brand new Galaxy S6edge (something like $850 at the time) without giving them any money up front and an unlimited everything plan for $50 a month. The phone is $25 on top of that, with yearly upgrades or I can pay on it for 2 years and it’s mine - so effectively just $600 for the phone and the only fees and taxes are on the $50 portion of the plan.
I pay the same monthly bill now, for a new phone and nothing down, as I was paying AT&T. The kicker is, AT&T never really gave me unlimited 4G - they throttled me whenever I used over 5gigs a month. No such thing with Sprint - and it’s faster. The best data speed I got with AT&T was about 6Mbps down and 2 up. My Sprint speed right now is 34 down and 10 up.
The only tiny bit of disappointment I have with Sprint is the voice quality could be better. Sprint to Sprint calls are freaky good HD, but others are a little tinny - though I haven’t had any dropped calls and I did sometimes with AT&T. It’s a very minor thing for me, though, as I use my cell for voice calls maybe twice a month! YMMV.