Unlike Europe, and I assume Oz, American GSM phones are network specific so you can't swap out SIM cards to switch carriers. Bummer, huh?
We have that problem with some phones, but I will explain shortly. I have a magazine (around here somewhere) from the US explaining how to unlock some of your phones. When (if) I find it I will post up some details.
But then again, the US wireless companies heavily subsidize their phones so that they are much less than the actual price. It's shocking how expensive "unlocked" phones cost sometimes. Do overseas carriers subsidize phones when their phones could end up being used on another carrier?
Yes we get some phones subsidized, but they mostly fall into 2 catagories. We have pre-paid or plan purchases. Most pre-paid are locked to a network they can be unlocked for a fee (detirmined by the phone company) so they are basically throw away. If you purchase a mobile on a plan, the phone is usually unlocked, but you sign up for a 2 year contract. If you want out of the contract you pay exit fees.
There are 3 major GSM phone carriers here, and most of the others smaller companies use these 3 networks. There is limited roaming between these 3.(basically dont bother)
So you can buy 3 pre-paid cards and use them in an emergency. The longest lasting pre-paid lasts for 12 months and you loose what credit you havent used, then you have to recharge it.
I actually buy my phones outright and dont sign up for a contract. That gives my the flexability to swap companies when they give me the @$%$s
Also if you add up the costs it can be quite scarry to sign up for 2 years so money wise I'm not far behind. Tried contracts, not for me and pre-paid is too expensive for what I use.
We also have CDMA but there is only 1 CDMA network and the others resell it.
We basically have little coverage out side of the metropolitan areas and some locals have had to get a phone with satelite backup, so they have either GSM or CDMA when they are in range but swap to satelite outside of that area.
If you want an unlocked phone, you could try is contact the importers of the phones direct and see what they can do, or order a phone out of Hong Kong from ebay (after checking the seller)
The other thing you could try is getting software to reprogram your phone and unlock it.
I read some where about someone who travelled from the US to europe somewhere and walked in and had his phone reprogramed and unlocked to use their local system. For a fee.