How to prevent iPhone from getting locked when moving to a different country?

I'll be moving to Sydney, Australia from India soon and I have an iPhone 7. Everyone is telling me that the phone might get locked when I move. Is there a way to prevent that?

Do not use the sim in that country and the cell will not be locked.

When you purchase a phone on a contract OR on an installment plan from postpaid carrier OR purchase a phone from a prepaid carrier, your phone will be locked to that carrier. HOWEVER, you can submit an unlock request if certain conditions are covered.

Generally…

For postpaid (contact) carriers, you will need to complete one of the following:
A) Complete your contract
B) Pay your Early Termination Fee
C) Pay off your Installment Plan COMPLETELY

AND have your account in good standing (no past due balances). If you have a past-due balance, you'll need to wait a day after you resolve the balance (to allow your carrier's automated systems to see that you're back in good standing… Even if you're account is canceled).

For Prepaid carriers, you typically need to have 12 months of service with the phone.

This also runs under the assumption that you have NOT reported your phone as lost or stolen to your carrier.

SPECIAL EXCEPTION: Most carriers will allowed military subscribers (at least in the US) to waive these requirements if they are being deployed outside their country. These subscribers MUST provide proof of deployment to obtain this exception.

Once these conditions are met, you can typically contact your carrier OR visit their website to submit an unlock request. This typically requires you to submit your name, e-mail address (for correspondence) & your iPhone's IMEI to the carrier & generally takes around 2 business days (sometimes this can take as little at 5 minutes). Once you get the approval, you generally need to wait a day to allow your carrier's automated systems get in touch with Apple's systems to give them the OK. Then all you have to do is to connect your iPhone to a computer running iTunes to do a backup (if you want to retain everything on your phone) & restore. As part of the restoration process, your iPhone gets unlocked (by some technical magic with Apple's servers).

They mean sim lock, not as in lock like the lock screen where you can't use it at all.

If your phone is paid off, then it should be carrier unlock. If you haven't finished paying it off, then you can't use another carrier's SIM card but it doesn't hurt to ask your carrier if it can unlock it. If you've been with them for a long time or you're near the end of your payment, it'll probably unlock it.

Let's assume that it's carrier unlocked, then you have to think about whether your phone is cdma or gsm or both. If you bought the sim free version from Apple then it should be gsm and cdma. If you got it under contract with AT&T or t-mobile, it's gsm. If you got it from Verizon or sprint, it's cdma unless you got the Verizon version from Apple, in which case it's both. Not sure if it's both if you get it from a Verizon store. Different carriers uses different bands so if your phone is gsm then you need a gsm carrier.

The phone would not be locked because you moved. Its either locked or not right now. If it is locked, then it wouldn't work with Australian SIM cards. It would need to be unlocked for that to happen. If it is unlocked, you're set.