Using WhatsApp while in another country
WhatsApp Messenger uses the same internet data plan as web browsing and email on your phone. If using your cellular data while roaming will normally result in additional charges, you may be charged extra by your mobile provider for using WhatsApp while roaming. Contact your wireless carrier for details about international-roaming countries, SIMs, rates, and policies.
If you do not have an international data plan, turn off Cellular Data and/or Data Roaming to avoid data roaming charges in iPhone Settings > Cellular > Data Roaming.
For iOS 6 and below: iPhone Settings > General > Cellular > Data Roaming.
Using WhatsApp while your phone is connected to Wi-Fi should not incur charges from your carrier. Please note that some Wi-Fi networks may have charges or usage fees.
Even with your SIM card removed or your cellular connection disabled, you can continue using your existing number in WhatsApp. If you have a local SIM card while travelling, you can use the change number feature to migrate your account to your new number.
WhatsApp Support Team