Can I put my cricket sim card into a straighttalk phone?

I recently just bought an iPhone 6 from Straight talk. I'm currently with Cricket wireless and I have a LG Stylo 3. I was wondering could I just insert my sim card from my from current phone into the iPhone? Will it work still? Or do I have to get the iPhone unlocked. I've read a lot of mixed answers. Don't really know what to do.

Good

Unless you bought the phone unlocked it will be locked to the network work you bought the phone from and will only work with that networks sims there may be restrictions on getting the phone unlocked