Can I change the SIM card on an iPhone 6 to 5s with no problem?

Skyrocket45 wrote:

Will the carrier get messed up with which phone?

Nope. The Carrier information, number and service is contained in the sim card.

Swapping the sim cards will swap all carrier info, to the other iPhone.

Both the iPhone 5s and iPhone 6 use use the same sized sim card. A Nano sim.

You can use the sim card in either iPhone assuming either the receiving iPhone is unlocked, or if locked, it is locked to the carrier the sim card is for.

Other than that, there should be no issues swapping sim cards between iPhones.

Skyrocket45 wrote:

I Just wanted to know

So long as both phones are with the same phone carrier.