LG MM-535 Owner's Manual page 13

If you received your phone in the mail or purchased it at a Sprint Store,
it probably has already been activated. All you need to do is unlock
your phone.
If your phone is not activated, please refer to the Start Here Guide
included with your phone.
Press and hold
Slide the phone open and select
Enter your four-digit lock code. (For security purposes, the
code is not visible as you type.)
to turn the phone on.
(right softkey).