Using WhatsApp with a SIM card for America
Keep your own number when using WhatsApp with a sim card for the USA
With a prepaid sim card for the USA in your phone, you wil get an American phone number. Someone calling you will also have to call this new number. However, this does not apply to WhatsApp!
On WhatsApp, you can continue to use your own phone number, as you are used to. Once the app realises there is a different SIM card with a new number apllied to your the phone, it will ask whether you want to use the new or the old number. If you choose your own number, nothing will change for you on Whatsapp. You will be able to send messages and make calls via Whatsapp as usual.
When you put your old SIM card back in your phone after your trip, you will get your old number back. You will be able to make calls on this number again and WhatsApp will remain as it was.