Not illegal, but unlocking the phone by jailbreaking voids your warranty with Apple and may get you in trouble with your carrier.
No they aren't illegal but once they are unlocked the warrantee for the phone is no longer valid. Yet with an unlocked phone you can get apps that you want without any restrictions.
You can visit apple.com or visit a local apple store for unlocked iPhone.
When you say "unlocked phones" I am assuming you are talking about phones that have been hacked into. The Apple iPhone can be unlocked using an App called Handbreak. It lets you modify your phone beyond what Apple allows. If you unlock your phone, there is a good chance that the warranty on your phone will be void. I do not recommend to unlock it.
There are many online options available for unlocked GSM phones, such as http://www.puremobile.com/ or http://www.cellhut.com/. You can also search eBay or a thrift store.
Yes you can get unlocked phones online which can be used on any carrier. One of the best places to find unlocked phones is ebay.
does cell mart sell unlocked phones
no
AT&T/Verizon allows you to use an unlocked phone. Also there are many models of the Apple IPhone. AT&T is less expensive than most of the unlocked phones. The company pays part of the cost.
Buying new, unlocked phones or unlocking your existing phone is legal in the U.S.
You should be able to find information on unlocked phones on the company of your phone's official website, or if they do not have anything about unlocked phones, you could talk to customer service.
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/.
only unlocked phones