Unlocking Bad ESN / IMEI / MEID For A Rookie

I have an iPhone 4s with Verizon, has a sim but it also has a bad imei/esn. When I jailbreak this phone using evasi0n, will I be able to use on other GSM carriers or not. Either way do I need to remove Verizon SIM before jailbreaking, or do I need to jailbreak with another carrier's SIM installed? How exactly does this unlock thing work?

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