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1) I posted this a couple months ago:

You can buy SIM cards in the US. There are a couple of caveats, though:
1) You have to make sure your phone will work in the US. Our GSM frequencies (850 and 1900 MHz) are not the same as those used in Europe (900 and 1800 MHz). If your phone will not operate on our frequencies, nothing you can do will make it work over here.
1a) Obviously, if yours does work on our frequencies, it must also be unlocked to do so. This may be a software issue, it may be a hardware issue, depending on your phone.
2) We have two standards here: GSM and CDMA. CDMA is more popular, and generally has wider coverage (though this is dependent on network). AT&T and T-Mobile are the only two major companies that use GSM. AT&T is larger.

You may consider buying a pre-paid phone when you get here instead. No issues with network standards, cross-operability, etc. They are cheap, and easy to find.
When you are done, head to a local post office. They have envelopes for used cell phones (if you don't see them out, ask).

To add on that, in the US you pay for all calls, incoming and outgoing. AFAIK, only regular customers with specific plans may have options where they don't pay for some incoming or outgoing calls.
You will just have to deal with the expense.

Two things about coverage:
1) Because it bears repeating, CDMA generally has better coverage, however coverage for both standards is completely dependent on provider and location. These are things you will have to look up; and
2) There are just some places where you will not get coverage. Period. This includes much of the west, and many national parks.

You will not find SIM cards at newspaper stands, and likely not at airports. You will need to find company stores/kiosks, or happen to find the right electronics stores that sell them (like Radio Shack). Google for locations.

2) Maybe, but likely not. Check the coverage maps for each company.

3) No. But you can find them if you look.

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Pre-paid phones, with sim card installed are available from Walmart - which is everywhere. Tracfone is one cheap company.

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For Hawaii (and most of the U.S.) your coverage depends on your phone company. You will have to look at coverage maps for each company to see if you can get it in the remotes areas. I don't think Maunaloa will be a problem.

I have moved frequently between the US and Int'l and I do not like to purchase new cell phones or special tracphones and prepaid stuff I feel is a waste to get a new phone. Also, you never know what service company that phone is buying from or know your coverage. I only ever just purchase pre-paid GSM SIM cards from the right company to install in my phone, similar to what is standard in Asian markets.

Here in Hawaii two companies offer SIM cards that you can buy pre-paid: T-Mobile and AT&T. You can purchase them online the 'SIM activition Kit' or walk into a store and they will give you a SIM card. I don't remember if there are kiosks at any airports in Hawaii. Usually you pay $20 and get $20 worth of credit or a similar deal.

The rates to call international are horrible on these cards. Get another int'l card w/ a local contact number if you intend to call home. and I repeat the warning of the first poster you pay for both Incoming AND Outgoing calls in the United States and texts.