So far I tried: Redpocket / T-Mobile (30$ Walmart/online plan) / AT&T Go Phone / T-Mobile Monthly plan / ...
All of them give you Voice Minutes, Data and Messaging. I just popped those SIM cards into my (unlocked) GSM phone and that was that.
I guess what you can't get are those 100$ / month with a "subsidised" phone plans. But I don't know why anybody would want these. Any of those options cost me less than 55$ / month. I'm currently on the T-mobile 30$/Walmart/Online plan. 100 minutes talk, Unlimited text, First 5 GB at up to 4G speeds. No need for any of the mentioned things.
p.s. and the ones I picked are only a small subset. H2O and Simple are even available at a lot of supermarkets.
I have a T-mobile Sim for visiting the US. The plan is 2USD per day for unlimited calls and 2G-speed data, and I only top up the amount I need each trip (11 days means I top up 22USD).
If I were to get new SIM card each time I went the cost would be similar, if I were able to get a free sim (with no credit) or more if they don't have a free sim offer at the time.
Is there some deal with new sims of which I'm not aware?
If you need to do this regularly, I recommend keeping an eye on slickdeals.net, as people post there whenever T-mobile do their free or 99 cent sim promotion. IIRC you can order two sims at a time, and it seems like you get a cryptic error message if you've ordered a free sim from them in the previous 12 months.
Can a tourist get a SIM card in the US?
Getting a SIM card in store seemed to require signing a multi-year contract, so I ran as far as possible before I could figure out whether they wanted my SSN or not.
These sorts of plans are gradually spilling over into the tech community, as those with the means to purchase their phones up front for full price, see the value of a contract-less plan.
Even on a T-Mobile prepaid plan, they insisted on an SSN after a year and refused to charge my Amex. I told them I was Canadian, so they asked for a SIN. They said Amex required it. Only after getting Amex involved did T-Mobile back down.
There's about zero risk for them on a prepaid system. The risk is someone trying to exploit a hole in their billing platform, which is really quite minuscule.
(I don't remember if prepaid wasn't an option or just wasn't as good a deal).
My father and his brother both 'ran away' from their (abusive) family when they were 16 and 15 respectively, in the late 60s. Bought a car with cash they had saved up, drove across the country, rented an apartment for a few years and worked various jobs before joining different branches of the military and eventually going to college.
A few decades later, I imagine this sort of thing as being near impossible for today's teenagers. Not because they are "wussier" or immature for their age, but because the world has changed and expectations that people have of teenagers and young adults have changed. Everything has more paperwork, everyone seems to expect background checks and credit checks. Teenagers and young adults seemingly need cosigners for damn near everything for their first few years away from home.
I had a lot of friction with this stuff in the 90's/early 00's when I was that age as my father's philosophy towards cosigning was "tell them that you can afford it yourself, and them to go fuck themselves." As late as 22 years old I had landlords that were hesitant (although ultimately not unwilling) to rent to me without a cosigner, even though I was gainfully employed and had fine credit. Even for that age range a lot of them seem to think that people being dependent on their parents is the norm.
So if obtaining service is really not the problem what is? Quite simply the problem is that most of these prepaid services don't sell the phones that a teenager is going to want (smart phones in general but iPhones in particular). It's only very recently that these sorts of phones have been supported at all by the prepaid industry.
Even when the phones are supported the American phone market is distorted by carrier subsidies. Many people don't realize how much cheaper buying a phone and using a cheaper service can be. The prepaid market on the other hand is not significantly subsidized (if at all). So kids and/or parents don't even consider buying a phone outside of a postpaid provider on a contract.
It's possible to buy a used phone for a fairly reasonable price, but then you're dealing with a potential mess of issues. You have to make sure to buy a phone that your chosen carrier will activate. Even some seemingly compatible systems won't activate phones sold by the other (Verizon & Sprint in particular). The phone might work and be allowed by the provider, but not have the proper bands for 3G/4G service (some iPhones on T-Mobile). Your carrier might refuse to activate service since they might say the phone is still under contract or stolen. For that matter the phone might still be carrier locked to another provider.
Even if a teenager has the cash to pay for their plan they often won't have the cash to buy the phone they want. So I suspect a lot of parents buy phones. As others have pointed out a lot of the carriers have seemingly low charges for adding additional lines. So combined with the additional line charge and the subsidized cost parents just add their kids to their own postpaid service.
Often times though these additional line fees are misleading, since they typically tack on more fees for data capabilities. Which racks up the price. Since this isn't clearly advertised a lot of people don't understand it and don't consider it in price comparisons with prepaid providers.
So in my opinion it's almost entirely about phone selection and phone subsidization. Those things drive tons of people to postpaid plans which of course do have the issues you point out. But as soon as you are willing to accept less fashionable phones those sorts of issues erode and there's nothing stopping a teenager from obtaining service (or for that matter even paying for a phone).