Sprint and Verizon will offer the iPhone 4S with an unlocked micro-SIM card slot according to information given to Macworld. The iPhone 4S is the first iPhone that can be classed as a world phone which means it has a GSM and CDMA radio. This is particularly useful if travelling overseas where CDMA networks are few and far between.
In simple terms, this means that users of Sprint or Verizon who buy an iPhone 4S and travel overseas will have the ability to install a local micro-SIM card in their phone; to use on GSM networks. AT&T will still offer the iPhone 4S with a locked micro-SIM card slot; which means users can roam on overseas GSM networks but do so via AT&T agreements with local carriers. This leads to a huge increase in call and data charges with this method.
If you use Sprint or Verizon and travel overseas, having an unlocked phone could save you a considerable amount of money. The downside however is that your number will be different when using a local micro-SIM card. Sprint’s iPhone 4S will be unlocked from day one but Verizon will do it on request after 60 days; as long as your account is in good standing.