I wanted Straight Talk to connect me to Verizon's network. It doesn't work that way they say -after several emails.
The program assigns you AFTER you register. The CSRs say they can't tell in advance. But know CDMA is dying out and your phone even if had CDMA likely has LTE 3 or 4. Most likely Straight talk will assign a Verizon iphone to ATT because it is their cheapest contractor. Verizon charges Straight Talk much more. Also Verizon has admitted that if a cell gets too busy, Straight Talk and other similar virtual carriers will be given lower priorities.
For details go to HOWARD FORUM.
I wanted to be assigned on Straight Talk to use Verizon. I had iphone 5. The likelihood of me being assigned to use Verizon was next to zero because I[my iphone 5] could use GMS, or LTE etc with ATT or T-Mobile.
FYI.
Also All iphone 5S phones from Verizon are UNLOCKED, 5C and just plain 5 iphones too. Why. When Verizon wanted to buy additional LTE spectrum the US Government made unlocking every phone they sold a condition of giving Verizon the spectrum.
Straight Talk is inexpensive compared to Verizon. $35 unlimited everything but for Bring Your Own Device folks only the first 5GB data is LTE4 the rest per month can be as slow as 56kb/sec. according to warning on Straight Talk site. Verizon for a single customer on prepay is $45/month with 1GB data however additional 1GB if you allow auto billing to debit/credit card.