Unlocking CDMA PhonesCDMA phones can be unlocked technically. But not in the same way most people thinking of GSM/TDMA and iDEN unlocking. CDMA mobile phones don't use a SIM card, they're "hardwired" to the provider that sells them. examples are: Verizion Wireless CDMA Mobile Phones or Sprint-Nextel and their CDMA Cell phones as well as other smaller carriers. Because of this they can only be unlocked by the provider with a special code that they absolutely will not give out over the phone unless you know someone on the inside.
As opposed to a At&t Wireless (formally Cingular), T-Mobile or Cellular One customer who can call up these GSM Carriers and get a unlock code over the phone. So He/She can use the cell phone over sea's (Note the cell phone much have the right frequency built in to be used over sea's) More About Gsm Cell Phone Frequencies . GSM Cell Phones can most of the time be unlocked remotely. While a CDMA phones require a bit of 'reprogramming' to unlock which can also be done remotely BUT it's not as simple as calling your provider and getting a code over the phone.
Why CDMA phones aren't unlockedIt is impractical to Unlock CDMA cellPhones. Sprint wont activate a non-Sprint Phone, so an unlocked CDMA phone would be useless to a Sprint Customer. Verizon will sometimes activate other CDMA provider's unlocked cell phones. i've witnessed this. But if you are an average joe with no connection in Verizion they will probably give you a hard time, try to sell you one of their cell phones etc. Although if a potential customer goes into a Verizon authorized Dealer Store and not an Official Verizion Store they may be easier on the customer. Their main goal is to sell Verizon service. Even if they lose money on the phone they make commission on the services plan and extra they can convince the customer to buy. Most of the time if an unlocked CDMA phone is activated with a provider from other than who it was made for a lot of the features will not work correctly or unless someone with quite a bit of technical knowledge reprograms the phone to your provider's specifications.
Note: Spread-spectrum techniques (used in CDMA) are methods by which energy generated at one or more discrete frequencies is deliberately spread or distributed in time or frequency domains. This is done for a variety of reasons, including the establishment of secure communications, increasing resistance to natural interference and jamming, and to prevent detection.