Activating an iPhone on Straight Talk via SIM card?

If I were to buy an iPhone 5 from Straight Talk (ST) and not activate it via the CDMA method, would it work if I put a ST SIM card into it? I already have ST service with a SIM from ST. If I buy the iPhone, I would cut my SIM to a nano size and use that in the iPhone. Would my service still work if I cut the SIM properly? Also, if I decide that I don't want ST service anymore, would it be possible for me to get a SIM from a different carrier and use it in the iPhone or is it locked specifically to ST?

The iPhones are locked to the carrier but if you want an I phone you have to buy an AT&T version and buy an unlock and then you will be able to use it with any SIM card you want! And don't buy CDMA phones because most won't take SIM cards

"If I were to buy an iPhone 5 fron Straight Talk (ST) and not activate it via the CDMA method, would it work if I put a ST SIM card into it?" You can't bring your own CDMA phone and activate it with ST.ST does have phones that run off of Verizons and Sprints towers through CDMA but the phones were already manufactured through ST. If you want to put a SIM card into the iPhone 5, you would have to either get the GSM carriers (T Mobile and AT&T) and use their SIM cards. I wouldn't recommend AT&T as ST and AT&T are fighting over something and AT&T is throttling ST customers data and they quit selling AT&T ST sim cards.
"Would my service still work if I cut the SIM properly?" Yes it would. Text and voice would work but you would have to change the APN settings (ST will tell you how) to have MMS and data.
"Also if I decided that I don't want ST service anymore, would it be possible for me to get a SIM from a different carrier and use it in the iPhone or is it specifically locked to ST?" Yes it is specifically locked to ST. If you were going to do this, I would recommend to buy an unlocked GSM iPhone 5 because it would be the same price as the ST iPhone 5 but you could also change GSM carriers whenever you want to.