It is unlimited but the carriers either throttle the data after you use over a certain number of gigabytes, meaning they slow your data down after $x gigabytes or they “deprioritize” your data. Meaning that if you use over $y gigs and your local tower is congested, your data may be slowed down to prioritize other users.

For T-mobile, they deprioritize your data at 55GB. I’ve never seen it in practice. My older son who doesn’t live with us uses his phone as his only internet connection and easily uses 80GB+ a month. We were at an extended stay for 6 months while we were waiting for our house to be built, and we were going through 70GB each between my younger son using tethering for his PS4 and us using our phones as hotspots for an AppleTV.

YMMV. I had one of the old grandfathered AT&T 'unlimited' plans. Within a short time after they stopped offering this plan to new customers, we started hitting a hard throttle at around 10 GB or something ridiculous like that. Once we hit it (after about two weeks at that time), it made the internet practically unusable for the rest of the billing cycle. Forget about streaming music or games - let alone video - there was a long wait even for text sites to load.

We have since changed plans and I have been leery of the u-word ever since.

I had to use a hotspot for a month and I went through 100gb without trying. Big parts were the 1-2GB OS updates on various computers and phones that download automatically. Docker that pulls the entire world. Netflix and YouTube bingeing for a saturday afternoon. And at one point the PS4 downloaded the Mad Max v1.06 update at a whopping 28 gigabyte without asking for permission.

Usually "subject to a fair use policy". In other words, it's limited, but they don't tell you the limit up front.

Typically you still have a limit on LTE. Something around 4GB of LTE data before getting dropped to UMTS with no cap.

UMTS is basically being capped though.

I have a 3G subscription and have no problem getting 10 megabit/s on tethering. That is enough for 1080p Netflix/YouTube and easily enough for webbrowsing.

Ah, my mistake, I switched GRPS and UMTS in my head. In my country, you are being capped to GPRS speed when your limit is reached.

Technically unlimited but usually throttled after ~10GB or so in my experience.

It is unlimited, but it's much slower after you hit the limit.