Please note Verizon & Sprint iPhone 4S is CDMA & GSM Compatible but Verizon and Sprint Lock their GSM Portion of the iPhone 4S (Sprint also does this with iPhone 5 but Verizon due to FCC rules & Regulations cannot so the Verizon iPhone 5 GSM portion is Unlocked meaning you can use it on any GSM Network in USA, Canada and world wide! whereas Sprint and Verizon iPhone 4S can only be used on International GSM networks as they have purposely put a block on all USA GSM Carriers)
Verizon iPhone 5 since it comes with its GSM Portion Unlocked can be used on AT&T and T-Mobile out of the box, But will not get LTE on AT&T due to not having the required bands.
Spring iPhone 5 will only work on International GSM Carrier networks meaning anywhere outside of USA.
Also what I meant was that there is no Network that you can run your iPhone 4S on which uses Verizon towers. Straight Talk uses AT&T and T-Mobile towers to provide its customer service. When you start digging in there is tons of information most people don't know about so I don't blame you and its a bit confusing at first.
Aww ok. Thanks for the explanation! That clarifies a lot!