sim card for iphone 6s

No iPhone 4 Uses Micro-Sim card, and iPhone 6s uses a smaller Nano-SIM card

Source:

Learn which size SIM card your iPhone or iPad uses - Apple Support

Call your carrier and arrange to get a Nano-sim card.

then follow:

Remove or switch the SIM card in your iPhone or iPad - Apple Support

Good luck!

Yes. But you need to make sure your new phone is unlocked onto any carrier in order for it to work, if it isn't unlocked you'll need to contact the carrier who locked the phone.

Example)

Your iPhone 4 has a Verizon sim-card but your friend is on AT&T and his phone is locked to that network, you must contact AT&T (This is just an example to try and help you understand, I'm not saying the phone is locked to AT&T)

Ijustwanttolookattheforums wrote:

Yes. But you need to make sure your new phone is unlocked onto any carrier in order for it to work, if it isn't unlocked you'll need to contact the carrier who locked the phone.

No, the iPhone 4 SIM is too large, as ckuan notes.

Example)

Your iPhone 4 has a Verizon sim-card but your friend is on AT&T and his phone is locked to that network, you must contact AT&T (This is just an example to try and help you understand, I'm not saying the phone is locked to AT&T)

The Verizon iPhone 4 was CDMA only and didn't have a physical SIM slot at all.

No, the iPhone 4 uses micro-SIM

iPhone 6s uses a nano-SIM.

Ask your carrier to send you one.