Unlocking is not illegal. Carriers lock the phones that they sell so that the consumer will be forced to use the phone on their networks. After the consumer has fulfilled the contract or paid the early termination fee the phone is his to do with as he wants. He can then get the phone unlocked. As far as the unlocking goes, you need to enter a code depending upon the
imei number of the phone.
And that oftentimes requires special equiptment to determine, or a phone call to the carriers customer service department.
The 850 mhz and 1900 mhz refers to the frequencies that the U.S. carriers use. Europe uses 900 and 1800 mhz. so their phones will not work in the U.S. unless the phones also work on the US frequencies.