Why are cell phones in the US locked?

What are the benefits of this? I know people in Europe and Asia like unlocked phones and I've heard that they have better phone service and faster data networks than us.

Locked phones are not compatible with other sim cards . If you unlock your phone, you can use it with any other GSM carriers internationally . To unlock your phone, use unlock code . You can get it from any of the online vendors like Unlock-Free.com to unlock it