blocked? by blocked im guessing your talking about carrier locked...well it depends on the basband and firmware its on but mainly the baseband....i would , if its not in 4.1 already, use tiny umbrella to update to 4.1 but preserve the baseband and then jailbreak and add unltrasn0w...
You need a baseband that is less than 05.14.02 and it can be firmware 4.1 you can use limera1n if you want. If I is less than 4.1 but more than 3.1.2 you can use jailbreakme.com