AT&T is the best prepaid SIM for the USA, Canada and Mexico.

You must follow instructions (here) to activate (takes about 3 minutes to activate the SIM one of the plans and add the Credit PIN which covers the cost of the plan).

We recommend the most popular plan the SIM+USD$50 credit PIN

SUMMARY
AT&T is the fastest and easiest network in the United States to be accessed by international phones (Most other US networks are slow, poor coverage or not fully compatible with international phones).

Pros
Great coverage and high speed 3G/4G/LTE data
USD$50, USD$65, USD$85 plans roam in Canada & Mexico

USD$50 plan - 8GB data (allows tethering/sharing data)
USD$65 plan - Unlimited data (but its speed is capped at 3Mbps & not allowed to tether/hotspot the data to other devices)
USD$85 plan - Unlimited data (allows tethering/sharing 10GB data in US)

Cons

International calls not included (but USD$5 call pack gives 250 min calling to international landlines). If you want the international call pack, add this direct in the AT&T portal AFTER you arrive in the States.

Activation takes a few steps, but we provide the most detailed step by step guide for you to activate prior to you leaving home, or alternatively we can activate for you (activation service costs AUD$20).

QUICK STEPS
1) Buy SIM and credit/PIN on dataGO - receive SIM in post & PIN via email
2) Online (few days before departure):

Activate SIM
Choose plan
Pay for plan with PIN (starts 30 days to use)

3) Land in US - activated SIM in an unlocked phone will auto connect on arrival

See activation summary in the tab above, or our detailed activation guide here.

Recommendation: The easiest way is to buy the SIM+PIN now, then activate and add credit/PIN online a few days before you leave. Simple :-)

SIM CARD SIZE

ALL SIMs are now TRIO SIMs - they pop out to any size required (Mini, Micro or Nano)

SHIPPING

Aust Express Post flat $6

International tracked flat $14

International courier $29

See more details on shipping information here

PLANS
Get the most from your smartphone we recommend the US$50 Smartphone Plan with Data (8 GB) - this is by far the most popular and best value plan for the average traveller spending a few weeks in the USA.

We don't recommend signing up for Auto-Pay as you need to enter you credit card, and get billed each month (hence why we use Credit PIN/top-up vouchers so you don't have to give AT&T your credit card and don't get any extra charges).

See plans below:
USD$30 - no included data
USD$35 - 1GB data
USD$50 - 8GB data (roams in Canada and Mexico)
USD$65 - Unlimited data (roams in Canada and Mexico/not hotspot)
USD$85 - Unlimited data (roams in Canada and Mexico/10GB hotspot US)

Or if you require more specific info/detail see direct on AT&T website here.

Plans include unlimited SMS to Mexico, Canada, Australia, UK and over 100 countries - see the full list here.

ADDITIONAL PREPAID DATA PACKS
Data packages are available .

- US$10 for 1 GB or $20 for 3 GB (with US$50 plan)
- US$5 for 250 MB (with US$30 plan)

INTERNATIONAL CALLING
International calls aren't included in the standard plans (national calls are, and local/international SMS is too). If you are planning to do lots of international calls with your AT&T prepaid plan, you get 250 minutes of calling from the U.S. to landlines in over 50 countries, including Mexico and Canada, from just $5 per month. See details on the international call packs available under the 'International Calling' tab on the AT&T site here.

If you would like a call pack it is easiest to add it once you have activated your SIM and are in the States. Login to the account portal (you have to be in US to do this the first time) and buy it direct with AT&T.
There are few call packs:

USD$5 = 250 minutes of international calls
USD$10 = 1,000 minutes of international calls

See details and the full list of available countries.
For Australia and New Zealand this only covers landline calls.
Packages are good for 30 days as long as your account balance is not expired. Standard rates apply if package is not renewed after 30 days. Also, feature package balance rolls over if renewed before expiration date.

If you don't use a long distance package, or are calling mobile numbers not included in the long distance package, you can see the applicable rates here. Calls to Australia are USD$1.09/min, same to New Zealand and to the UK USD$0.49/min.

AT&T has great network coverage and fast data speeds. This makes calling via VoIP Apps like Skype and Viber a real and popular alternative. These type of voice calls typically only use ~0.3/MB per minute (which if you have the $60 plan with 8GB data - works out at less than USD$0.01/min for data plus the small cost of the Skype call - typically AUD$0.02 - $0.10/min).

There is also now a USD$15 East Asia and India pack that will give unlimited calling to mobiles and landlines in a selection of East Asian countries and discounted calls to Australia. To make the call at the discounted rate you will still need some balance credit (ie buy the $15 call pack and then have $5 balance credit to make calls to Australian mobiles at $0.05/min):

NETWORK/COVERAGE
AT&T has one of the largest (& fastest) GSM networks in the US.
You can find more specific network coverage information direct with AT&T here.
An AT&T prepaid SIM will only connect to the network in the US, Canada and Mexico - not outside of these three countries.

SIM AND PLAN EXPIRY

All the AT&T plans (ie USD$35, USD$45 and USD$65 plans) expire 30 days from when they went live (they go 'live' when you add enough credit to cover the cost of the plan).
For most people who activate on the USD$45 or 65 plan, the plan is valid for 30 days, and the SIM will expire 150 days (5 months) after first activated.

Detail: There are two issues here: i) expiry from credit, and ii) cancellation of SIM/number. They have two different drop-dead dates.

i) Expiry depends on the amount initially added:
From $10 to $24 30 days
From $25 to $99 90 days
$100 and higher 1 year

ii) While cancellation happens sixty days after expiry.
That means, for example, if you initially added USD$60 the SIM is good for 90 days, but the number remains yours for another 60 days (150 days total). As long as you add money before cancellation, the clock starts over again.