In many countries, everyone uses WhatsApp. In the US, many people still use the phone's normal text messages.
SMS is a normal text message. Almost every US plan includes unlimited texts inside the US, so people text freely.
iMessage is Apple's messaging. Between two iPhones, messages show as blue bubbles and go over the internet. To or from Android they are green bubbles.
RCS is the newer system for Android-to-Android and Android-to-iPhone texts. It adds photos, typing dots and read receipts.
What this means: schools, doctors, landlords, delivery drivers and employers will text your US number, not WhatsApp. Turn on notifications for normal Messages.
When people use other apps
WhatsApp is common among immigrants and for international family chats. Many Americans do not have it.
Group texts are normal for friends and parents' groups.
At work, people often use Slack, Microsoft Teams or email.
Many Americans text before calling. A surprise call can feel urgent.
Short replies like "Sounds good" or "Thanks!" are polite, not rude.
Texting late at night is fine with friends but not with a landlord or boss.
Voicemail is still used. Set up your voicemail greeting with your name, so callers know they reached the right person.
Wi-Fi calling lets your phone make normal calls and texts over Wi-Fi when the cell signal is weak, like in a basement apartment.
iPhone: Settings, Cellular (or Phone), Wi-Fi Calling, turn on.
Android: Phone app, Settings, Calls (or Wi-Fi calling), turn on.
Enter your US address when asked. It is used to send help if you call 911.
Update the address when you move.
Free over the internet: WhatsApp, FaceTime, Google Meet, Viber, Signal, Telegram, and other apps. Both people need the app and internet.
Calling a landline or older phone: many US plans include calls or texts to some countries, or offer an add-on for a few dollars a month. Check your plan's "international" page.
Prepaid calling apps and cards sell minutes by the country. Compare the per-minute price and any connection fee.
Calling an international number from your plan without checking the rate. Some cost over $1 a minute.
Only checking WhatsApp and missing a text from your school or landlord.
Leaving an old 911 address on Wi-Fi calling after moving.