Hi all, I'm asking for my brother who will be travelling on his own, flying into Dallas Fort Worth. He wants to purchase a pre-paid 4G Sim for an Australian mobile phone when he arrives (airport or near hotel, don't know). Which company is better - AT&T or Verizon?

Also he is thinking of crossing the border into Mexico at Nogales, Arizona to do shopping for a few hours. Wants to know if it's safe.
Any other info would be useful, like are there queues of traffic, is there a bus or do you have to take your own vehicle (he is hiring a car).

Yes, Nogales is safe. I've been there several times (day trips from AZ) for medical reasons and day shopping, and never once have I felt unsafe in any of the areas I've visit on foot.

You park right by the border on the US side (Nogales AZ) and walk across the border. Don't drive.

Lots of medical tourists places (pharmacies & dentists) and gift shops, restaurants in town to walk to right across the border.

You take I-19 literally to the end and park in one of the lots visible in the map I'm posting.
The border facility is highlighted in green and there are easy to follow signs.

I think for some shopping, you might as well just walk. There is a bus, however, but it could leave you off farther from the shopping than if you walked. Depends where you want to go

https://tufesa.com.mx/

Thanks very much for the info on Nogales, very helpful. I'll pass it on. The other question - he wants to buy a SIM card on arrival for his phone. Which company is better (more coverage, better reputation etc) - AT&T or Verizon? Other ideas?

I'd go with ATT, but if he won't use card for long, either should be just fine. Nogales should be pretty safe, especially if you don't go to outskirts. Personaly advice would be to hire a car, especially if he doesn't want to spend extra time( I think there are a bus, but it's usually very crowded and slow).

TMobile has a cheap plan for mexico