Cell phone for Australia, New Zealand?

Wow! is this a can of worms. I would like to have cell phone coverage in Australia and New Zealand while there. I have never had a cell phone and looking to get one that works in the U.S. as well. I am learning the hard way this is not simple. Let's see, you need a phone, but which one? Turns out an "unlocked" international phone GSM is required for overseas; most U.S. cell phones are locked and won't work. Then you need a Sim for each country visited (Australia and New Zealand, maybe U.S.) and you need a battery charger(plug adapter). Ok, a package deal is offered called AnZac at Telestial which gives you all these at $216 (a 49$ savings buying them separately is claimed). This is a pre-paid plan. You charge up the Sim as you need more minutes, buying cards at local tobacco shops.

The phone sold as part of this deal is the Siemens AF51, which sells any where from $99 to at Telestial $165. Reviews on this phone are variable. Now the Sims; Internationa sim cards don't work in New Zealand, a New Zealand sim card is $ 39 and an Australian one is $49; you must have both. Then there's the plug adapter for $14.99.

When I return, this phone won't work in the U.S., but apparently you can buy a sim for parts of the U.S. and then you have to buy a plan (prepaid perhaps?) with a local carrier. This will have to be researched as I go; this place looks like a start.

Then there's RangeRomer which offers a slightly different package; the so-called bread and butter package $149; the phone is the Siemens 870, which I can find no where else for sale..I wonder if it's strictly for RangeRomer? It looks like their world sim card will work in Australia and New Zealand and only the U.S. Virgin Islands, thus no possibilities in the continental U.S.

Any comments?