There is insufficient information about starting those plans without a credit history and what companies are easiest to deal with for immigrants.
It appears I was incorrect about a relatively simple solution to use a cellular telephone that we already have.
Nearly every single provider in the guide is prepaid, there is no issue of credit history. The other two providers that are postpaid still don't have a steep requirement because there are no contracts. If you have access to a hunk of plastic with a sixteen digit number that starts with the number 4 or 5 (Visa or MasterCard debit, credit, gift, or prepaid), you can pay for mobile phone service.
As for using an existing smartphone, so long as it's
carrier unlocked and has US GSM/UMTS/HSPA frequency support on the 850/1900MHz bands, it's entirely possible your parents might be able to keep using the phone they already have if they own a GSM world phone. As for your iPhone specifically mentioned, same applies, though T-Mobile MVNOs are going to work far better on the configuration and data end than AT&T ones. Long story short, you might discover it to be a PITA to configure your iPhone for mobile data and MMS on the AT&T MVNO plan I'm going to recommend in a couple paragraphs. Choosing an MVNO between the two networks for most people, however, is going to be dependent upon the geographical service area met. This really won't apply to your situation, though.
Next, if they don't want to spend a lot of money and can't go under contract (for obvious reasons), they're just going to have to get used to using less data. Welcome to America, our mobile industry is expensive and sucks! Good thing it's pretty easy to use less data
if you just plan ahead.
Lastly, given they're coming from China with no ESL experience, the best (and only real) carrier option is going to be Red Pocket - especially from a customer support standpoint as they have phone staff fluent in Mandarin. Don't bother with their GSMT plans despite the additional data, their auto-billing is still wonky on the T-Mo end, and the coverage is going to have a smaller footprint anyway. Instead, go with a GSMA plan (AT&T). All of their "unlimited" GSMA plans with data $40 and over has heavily throttled 2G data available after the high speed data allotment is used. $40 gets you 500MB of high speed data, $50 gets you 1GB, $60 gets you 3GB, and $70 gets you 4GB. Don't like the data allotment available at those prices? Again, see the welcome message above.
On the bright side (at least) to take some sting out of those data prices, Red Pocket's "unlimited" calling plans also include "unlimited" direct dial calling to both mobile and landline phones in China and Hong Kong and "unlimited" incoming international and 200 outbound international SMS text messages a month. None the less, they do claim to support carrier unlocked AT&T iPhones on their GSMA plans, but as I mentioned earlier,
the configuration process can be annoying compared to a T-Mo MVNO on the device.
That should get you.