Originally posted by: zerocool84
Some people want to be able to use a phone that is on AT&T on Tmobile or Sprint on Verizon or a phone that is not offered from any carrier here in the states but want to use that phone here. Also maybe they don't want to extent a contract but want a better phone so they will buy an unlocked phone. I've always bought unlocked phones because my plan wasn't offered any more and would have to move to a more expensive plan if I upgraded my phone.
That is a little broad of a statement. Yes an AT&T phone will work on T-Mobile but their 3G networks are completely different so you would lose that.
A Verizon phone will not work on Sprint period, Sprint will not allow it. Verizon will allow a Sprint phone but it is not the easiest process in the world.
AT&T/T-Mobile will not work on Sprint/Verizon or vice versa, they are completely different technologies.