Who is verizon going to unlock this phone for? Either I'm misunderstanding completely or there is a serious lack of understanding on how this phone works.
1) This is not a global phone. It has a sim card slot for LTE only. It cannot work on a GSM carrier and it only supports verizon's frequency for lte.
2) Since you would put it on CDMA straight talk, and since all cdma carriers even prepaid usually limit you to esn numbers that they recognize as their own branded phones, you likely cannot put this phone on straight talk even if it was unlocked for other cdma carriers
3) When verizon unlocks a phone they unlock global phones. They don't unlock cdma only phones nor can they unlock the cdma to work on other carriers, and even if they could they wouldn't do this because even when they unlock global phones, those phones are still blocked from at&t and tmobile.
4) It is possible to flash a cdma phone to a different carrier, but this is your job to hack and do, not the carrier's job. It is not something they want to help with since it would just cost them money to not have a customer.
5) Most importantly, since this is an LTE phone it may require a sim card simply to even activate and use on a network, however I have heard of lte phones on straight talk, though with some difficulty.
Anyway I'm almost 100% positive it would be impossible to put the stratosphere on straight talk cdma and am 100% positive it is impossible to put on their gsm.
Also further searching reveals that in general putting cdma phones onto straight talk does require flashing them over. If you want sprint's network it may be doable but you need a donor phone from what I can tell. If you want verizon's network then you will get kicked off it as all of their phones on straight talk currently have software called air tank on them which apparently straight talk can recognize. That is what i got from this thread linked below anyway. Good luck.
Android Straight Talk CDMA Flash