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 Data roaming to avoid data roaming charges.
To confirm that your data roaming is disabled:Android 2.1 and 2.3
Go to Settings > Wireless & networks > Mobile networks and make sure Data roaming is disabled.Android 4.0+
Go to Settings > More (under Wireless & networks) > Mobile or Cellular networks > and make sure Data roaming is disabled.Non stock Android
Look for Network or Data in your phone settings and disable the Data roaming option.
Provided you have Wi-Fi internet access and active WhatsApp service, WhatsApp...