Purchase IMEI unlock codes for the Samsung B3410 to allow it to be used on all networks.
A network lock, otherwise known as a SIM lock, is a control placed on the phone by the original network that sold it. They are able to do this because with the lock, they can then sell the phone for cheaper, offering the customer a better upfront deal. This lock does however stay with the phone permanently unless it is removed with an unlock code or software. Doing this is completely legal and won't impact your warranty in any way.
With all Samsung orders we deliver 4 different codes. The majority of orders will only require the Defreeze code and the Network code. The others are only required where the network that the phone is being unlocked from works differently that the main ones. In the same email that includes your unlock code, you will also receive complete instructions on how to enter it.