iPhone

Depends on how you buy it. In most cases it will be unlocked when you choose a carrier and you can even specify a sim free unlocked model that has no specific carrier.

See here: https://www.apple.com/shop/browse/overlay/iphone/carrier_unlocked

Will my new iPhone be unlocked?

Nearly all iPhone models sold on apple.com and at the Apple Store are unlocked. This means they aren’t tied to a single carrier. The exception is when you buy an iPhone with an AT&T Installment Plan. It will be tied — or locked — to AT&T.

• Your iPhone will be unlocked when you:
  • Choose any carrier and select One-time payment.
  • Choose any carrier and select Apple iPhone Payments.
  • Choose any carrier and either join or upgrade with the Apple iPhone Upgrade Program.
  • Purchase a SIM-free model. This is like any other iPhone, just without a carrier nano-SIM card.
• Your iPhone will be locked when you:
  • Choose AT&T as your carrier and pay with an AT&T Installment Plan.

Only if you purchase one that is fully unlocked. If they are models associated with specific providers, then they come locked to that carrier and contain an appropriate SIM. If your current provider is one of the four used by Apple, then buying one locked to the carrier you already use should work with your SIM.