Unlocking Nokia 3510 is a simple procedure, but it requires a specific unlock code to remove network restrictions put in place by your wireless service provider. You can find an unlock code generator for Nokia on websites like GSM/Unlock, Peters 1 or Unlock Nokia Free. These websites will give you a couple of free unlock codes to try on your phone. Keep in mind that these codes will not necessarily work, and you always run the risk of permanently locking your handset. To unlock a permanently locked phone, you will have to rely on a technician.
Find you Nokia 3510s IMEI number. Usually, it's found on a sticker beneath the phone's battery. If you can't find it there, type "*#06#" on the keypad and the phone's screen will show you the IMEI.
Visit a website that provides free unlock codes for Nokia 3510. (See Resources.)
Provide the phone's IMEI number to the website. Also, specify the network provider the phone is locked to.
Write down the list of unlock codes provided by the website. You will have to try a couple of them until you find one that works.
Type "#PW+CODE+1#". Keep trying different codes until you see the message "SIM Restriction Off."