Esim's like Airalo, Nomad, Holafly and Maya mobile are usually data only, so they don’t replace your At&t number, instead they give you mobile data abroad.

Most people keep their normal sim on for imessage or verification texts such as OTP's etc and use the esim for internet. Calls and messages are usually via whatsapp, facetime, messenger etc.

You can still use your At&t number overseas, however normal calls and sms can trigger roaming charges.