USA Visit

Most of this was already asked and answered 

https://forums.att.com/t5/AT-T-PREPAID/Visiting-USA-for-a-month/m-p/5398663#M67640

Plans are here:   https://www.att.com/prepaid/plans.html

1. Can I use iPhone's 'Personal HotSpot' feature on a prepaid mobile SIM? $35 or $45 plan

(tariff means tax). 
2. Which tariffs tier are available for unlimited calls to USA (mobile and landline)?  All of them 
3. Is there a tariff or bundle which gives me a package of calls to EU, specifically to Malta?  You have to purchase an international package and then will be charged a small pay per use charge.  

Mobie Wifi Services
4. Can I purchase a Mobile Wifi SIM (Data Only SIM) as a SIM only without
the device?   Yes, already asked and answered
5. Is there an Unlimited data version of Mobile Wifi SIM (SIM only) on prepaid?  No, already asked and answered.

General
6. These prepaid AT&T SIMs, are they GSM and which band?  Yes, already asked and answered

ATT operates on 3g bands 850 and 1900. LTE 2,4,5,12/17 and 30
7. Does AT&T give coverage across the USA including New York City,
Niagara, Washington DC, Florida?   Yes, already asked and answered.  

READ YOUR PREVIOUS POSTS............

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Regarding the answer to this:

1. Can I use iPhone's 'Personal HotSpot' feature on a prepaid mobile SIM? $35 or $45 plan

This doesn't meed my requirement as these plans are not valid for my Personal HotSpot use because they are only 1 GB or 6GB of data.

Can I in some way (maybe via a bundle) have a phone line for iPhone which gives me a Personal HotSpot and unlimited data? If yes which tariff will that be?

@robbierincewind

No.  ATT does not have a plan at all that allows unlimited hotspot use.  The prepaid plans for data only are as listed in the link.  

No US carrier allows data only devices to have unlimited prepaid data.  Most also do not allow postpaid unlimited on data only devices.  And you won’t qualify for a postpaid plan.

@robbierincewind

And yet for a only $10 more you get 6 times more data on the phone to use as a hotspot.  

You should be getting the $45 phone plan and add data at $20 for 3 gigs of data.  

Cost per gig $7.22 for 9 gigs, $7.04 for 12 gigs, etc.  As opposed to $10 per gig in the mobile hotspot.  

So I gave information, now I’m giving advice.  DONT GET A PLAN FOR THE MOBILE HOTSPOT. Get a plan for the phone and add data at the $20 for 3 gigs as often as you need to.

Unless you are traveling with many people and need them to use the hotspot when your phone is not around if you separate, there is no reason to buy a plan at 25% more per gig for a mobile hotspot.  Your phone will be capable of providing a hotspot, at the same time you use it for talk and text and data on the phone.  

big BIG thanks for your support and patience. Much appreciated.