Depends what you mean by "Blocked"
Phones are usually blocked when they have been reported lost or stolen.If this is the case then there is no legal way to unblock it.
If you have been locked out because you have inserted an incorrect PIN number then you need the PUK code which should have been included with the manual or paperwork that came with the phone.If you dont have this information then your service provider may have instructions on their website on how to restore the phone.
The only other alternative is to ring the mobile service providers helpline and get the PUK code