Check your phone supports the 850 MHz and 1900 MHz bands (most major ones do) and is SIM free and you'll be fine.

What does that mean, is sim free and I'll be fine? There's a sim card in my phone, for my current carrier.

Some phones (especially in Europe) are locked to your current carrier so they won't work with a different operator (i.e. you can't replace the SIM and expect it to work). This tends to be when you get the phone for free (and they want to tie you into a contract).

You can get them unlocked at markets and sometimes online so that they will work with all mobile networks.

I believe iPhones etc are all SIM free (or unlocked) when you buy them.

Sorry: By SIM free I mean not locked to a particular network.

If you create an prepaid account you will get a free sim card

I am from Australia and have investigated a few things.

I have an unlocked GSM phone that I bring with me. I also bring a $14 Nokia pre-paid phone I bought in the US (whose freqs don't work in AU).

Since I come at least once a year, I bought a T-Mobile SIM for around $25 and $100 worth of credits to get a "Gold" status, which keeps the number alive as long as I recharge it once a year. One of the first things I do in Vegas is to go to the Boulevard Mall (not just for the recharge) and buy $10 worth of credit and apply it. Sometimes I buy another credit to keep in my travel folder, in case I am going somewhere else and wouldn't have time to shop.

The T-Mobile pre-paid has no data included, so lately I am studying discussions in an Aussie forum where there is a lot of info on this. The wisdom of the crowds is to get an AT&T SIM (there are many to choose from) that costs around $11 from entrepreneurs on eBay and elsewhere, then put about 500 MB of data on it. This will let you do a little bit of FB/4SQ etc without worrying. Some people buy a monthly plan with 2 GB data and cancel it after a month. This trip will use my iPhone as a hotspot for my iPad and will use the AT&T SIM for it. I will keep the T-Mobile phone for calls since my regular Pubcon mates have that number.

Just guy a $20 disposable cell phone from Walmart or someplace in the US. They come loaded with time to use.

I now have an AT&T SIM for my iPad2 and have signed up for a monthly plan which gives me 2 GB data for $29.95. I will cancel when I leave.

Ring your carrier and say you are travelling and need to use a foreign SIM. Chances are high that they will unlock it for free.

Unless you're coming from North Korea or some other hostile country, I find it hard to believe that your country has no roaming agreement with the US.

Roaming charges can be very high, so getting a US SIM makes sense, especially for data.

I am not sure, Is prepaid Micro-sim available at SFO airport? It quite annoying for using iPhone 4s that require to find micro-sim. :(

Where I live, the two main carriers have quite different options for using your phone outside the country.

The fact that I could get a pay-as-you-go plan that worked in the US was the primary reason I chose my current cell provider (Rogers).

It's easier for me to just pay the occasional roaming charge than to fuss with sim cards etc. or trying to buy a local phone.

Nuttakorn, the pre-paid microSIM from AT&T will only give you 500 MB of data for $29.95, whereas a monthly plan costs the same, as long as you cancel before the end of the month.

I doubt you will find anything useful at SFO that you can't get cheaper at Walgreens in LV.

Check out this thread [forums.whirlpool.net.au], which I used to make my purchase. Given the lack of time, I suggest you plan a visit to an AT&T store. T-Mobile doesn't have anything comparable for visitors. The cheap SIM I have does not have data, hence I am also getting one from AT&T.

Using data roaming to do casual surfing/tweeting/4SQ could cost you several hundred dollars. Been there, done that.

Thanks man Nallawalla. I will try to get AT&T. Last year I got T-Mobile, only got GPRS.