How to jailbreak cspire iPhone 4?

I have an iPhone 4 with iOS 6 and I need a call blacklist app which is not available unless I unlock my phone. How can I do that? I'm with cspire and its a company that serves southern states. CDMA

Added (1). Do I have to have a computer to do it. I'm using the Internet from my iPhone…

Iblacklist can be used with jailbroke iphones, locked or unlocked doesnt matter.
click charts, iphone, firmware then follow directions to jailbreak

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