You have a lot of options since your device is a Straight Talk device. Straight Talk is compatible with all carriers making your switch easy. Their phones were wired to be compatible with both software technologies making the switch to and from their company very easy. You do need to check with them the specific type of phone it is - GSM or CDMA
Now about the SIM card, your ZTE device has a slot for a micro size SIM card.
On the Defense Mobile website, under their BYOD tab it explains how to bring your device to Defense from each carrier on the market!
STEP 1: Check if your phone is eligible. Here is an overview by carrier:
AT&T: All unlocked AT&T devices are supported on Defense Mobile. All you will need is a Defense Mobile GSM (A) SIM Card and a plan
T-Mobile: Unlocked T-mobile devices are supported, you just need a Defense Mobile GSM (A) SIM Card and a plan.
Sprint: Many Sprint phones are supported. To determine if your Sprint device is supported please click here. Please not that this is a preliminary check, if you submit a Support Ticket with the IMEI/MEID of your device we can give you a more definitive answer.
Verizon: All 3G and 4G Verizon devices are able to be used on our CDMA (V) network, as long as all Early Termination Fees and obligations to Verizon are paid. Additionally, the Nexus 6 and all iPhone 6, 6 Plus, 6s, 6s Plus devices can be used on our CDMA (V) network. To get started, you will need a Defense Mobile CDMA (V) SIM Card. If you have a 3G Verizon device, you can simply log in and activate it (no SIM required).
All Other Carriers: Please identify if your carrier is GSM or CDMA first (you can check here).
- All unlocked & off-contract GSM phones will work - you just need a Defense Mobile GSM (A) SIM Card.
- For CDMA phones, if you know your carrier uses the Sprint or Verizon network you can follow those instructions. Please note that we cannot activate Virgin Mobile devices.
- If you still have questions, please submit a support ticket here.
You will need to make sure your device is unlocked and simply order your SIM card and wait for it in the mail to complete your activation and service with Defense Mobile!