Ok. this is something that I was wondring for a long time, and now I'm finally going to ask this, because it's driving me crazy. I was wondering this generally for all phones, but also specifically for iPhone since I'm considering it.

What is the physical difference between a phone that you get with a subscription (like a two year plan where you pay monthy bills)and a pay-and-go phone where you can recharge your sim card with money (possible unlock it and use sim cards from different countries)?

Does a subsription phone have a sim card? (So, say, if I bought one like that and paid bills for 2 years, would i be later able to unlock it and use other, rechargable sim cards like in a pay-and-go phone?)

I would be very thankful for any anwsers and tips