Can I use an iPhone I purchased on another network on Meteor?
Yes you can once the phone is unlocked.
If the phone is locked you will need to contact your current provider and request an unlocking code from them. Your provider will ask what type of iPhone you're using, and for your phone's IMEI number (which you can get by dialling *#06# into your phone).
iPhones purchased through the Apple online store aren’t locked to any network so they can be used immediately on the Meteor network.