iPhone SIM Card
It was recently announced by Apple that the company will offer an unlocked version of the iPhone 4 starting at $649. The phone will work with any GSM carrier SIM card, which is a useful feature for those who frequently travel overseas. It makes it easy for travelers to buy a prepaid SIM card from local carriers in their destination country so they can pay the same rates that people within that country are paying.
Most phones sold in the US are sold locked to one carrier, so they can't use SIM cards from other networks. While the unlocked iPhone is more expensive to purchase upfront, it could be worth it for frequent international travelers. The savings you get by using local prepaid cards instead of your home network roaming plan can be upwards of 50%.