Your bank, email, government accounts and messaging apps at home probably send one-time codes to your home number. If that number is canceled, you can be locked out of your own money.
Keep the home number working
Before you leave home, ask your carrier for the cheapest way to keep the number active: a low-cost plan, a "parking" plan, or a prepaid top-up every few months.
Ask how long the number stays alive without a top-up. In many countries, an unused prepaid number is canceled after some months.
Put a reminder in your calendar for each top-up.
If your phone holds two SIMs, keep the home SIM inside with data roaming off. Codes by text usually still arrive.
Ask whether receiving texts abroad costs money.
Change the phone number on each important account (bank, email, Apple or Google account, government portals) to your US number, or add it as a second number.
Where you can, switch two-step login from text codes to an authenticator app. It works without any SIM.
Save the backup codes each service gives you. Keep them on paper at home and in a password manager.
For WhatsApp and similar apps, you can keep your home number as your account even after you get a US number, as long as you still control the SIM for re-verification.
US phone numbers are reused. When someone cancels a number, the carrier must wait at least 45 days, then can give it to a new customer. So your new US number probably belonged to someone else before.
What this means for you:
You may get calls and texts for the old owner (doctors, debt collectors, friends). Reply once "wrong number" to real people, then block. Do not share your details.
An app may say your number is "already in use". Contact the app's support to move it.
If you lose or cancel your US number, someone else will get it after about 45 days, including your codes. Before you change numbers, update every account first.
Before you change or cancel a US number
List your accounts that use it: bank, credit card, school, employer, health insurance, USCIS online account, apps.
Update each one to the new number.
To keep the same number at a new carrier, port it: give the new carrier your account number and port-out PIN from the old carrier. Do not cancel the old plan first, or the number may be lost.
Letting the home number expire in the first months because you were busy.
Turning on data roaming for the home SIM and paying high fees.
Canceling a US plan when you go home for the summer. Many carriers have cheap plans you can pause or keep at a low price.