Can I switch my Verizon iPhone to StraightTalk?

I have the iPhone 4 for Verizon and I'm switching over to straighttalk. How do I switch it over without having to get a new phone?

You can't, straight talk is a GSM company an uses SIM cards, Verizon uses CDMA and no SIM cards, however there are prepaid Verizon compatible carriers too such as Page Plus

Don't go for StraightTalk GSM, go for StraightTalk CDMA. Then you can get your Verizon iPhone 4 flashed to StraightTalk. You can mail this person (arghyle@rocketmail.com) who can help you with the flash.