Verizon Plan to Prepaid... unlocked?

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I'm planning on switching my Verizon iPhone 4s from a monthly plan to prepaid. Just wondering if this requires it to be unlocked? I know that may be REALLY dumb but... I don't know! So I thought I would ask the experts.

It's my understanding, too, that the 4s will only work on Verizons specialized version of CDMA (maybe a bit of misinformation there)... plus I do like Verizons service, just really need to go to prepaid.

My contract is almost up and looking at other options.