Yes it is. They are generally as reliable as a normal cell phone.
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You can visit apple.com or visit a local apple store for unlocked iPhone.
You can buy unlocked phones from internet sellers. For example, http://www.amazon.com/Unlocked-Phones-Accessories-Cell/b?ie=UTF8&node=283273011 and http://www.cellhut.com/.
You can buy cheap unlocked phones at retail electronic locations such as Best Buy and Future Shop. You can also buy these phones at big box retailers such as Walmart as well as at online shopping sites such as eBay,
Consumers may find cheap unlocked cell phones for sale on the Internet. A variety of auction-style websites and popular electronic merchants may feature cheap unlocked cell phones. If you buy an unlocked cell phone, you may be able to use the device on another service provider's network. You might be able to buy cheap unlocked cell phones through certain classified newspapers.
I would say that unlocked cellphones are probably safe, it's just that having your phone become unlocked voids your warranty. If you were to have any problems after unlocking your phone, the company would not fix it.
The best online retailers to buy a galaxy nexus would be www.amazon.com Cell Phones & Accessories Unlocked Phones,www.bestbuy.com Mobile Phones All Mobile Phones with Plans, or bestbuy.com.
The best place to buy cheaper sell phones that are unlocked and ready to buy are E-bay. You should always research the seller before buying anything to make sure everything is legit.
most phones are locked to a carrier. Some phones are unlocked and can be used as long as you have the correct technology. GSM, CDMA, etc...
Buying unlocked gsm phone is very legal. You can even figure out how to unlock them yourself.
1800Mobiles.com is one place to buy unlocked Verizon cellular phones. They have models from Motorola and Blackberry for sale.
The only way to buy unlocked phones is to find unofficial cellphone dealers who would unlock phones for you, and Nokias are no exception. eBay would be the best place to look.