Hi guys, I'm trying to buy an iPhone 4 and I found a guy off CL who wants to sell it for $50. The screen is cracked and he also mention last minute that it has a bad ESN. If I buy it, what can I do to it to make it useable for phone calls and texts? Will jailbreaking it an unlocking help? It was on the Verizon network but I want to use it for my T Mobile account. Can I do it and how?