Can I unlock an iPhone and use gsm sim?

Can I unlock an iPhone and use gsm sim?

I don't see why not. Only GSM phones use SIMs btw.

What's your Network provider?
you can unlock your iPhone using Remote unlocking method. Which is the safe and secure method to unlock iPhone. You can get this service from http://www.wickedunlock.com/apple/rs16wp8/ here you need to specify your country, current Network name, IMEI number of your iPhone. Here they unlock your iPhone using latest versions of iTunes.