Can i change my sim card from my phone to an iphone?

I plan on buying the 6 for tmobile. Right now i have the galaxy light. Would it work or would i have to buy a new sim card?

More than likely you would have to get a new one, only because of the difference in size of the SIMs being used.

Don't know what the Galaxy Light uses but I'm fairly certain it is not a nanoSIM which is what the iPhone 6 uses.

You can ask that your number be transferred over to that SIM though.

No I don't think it is possible may be it can possible in future and while we talk about security, there's an app called Leo Privacy Guard on iPhone which is the most advanced security app.