The initial announcement of the partnership between WhatsApp and TextSecure ( https://whispersystems.org/blog/whatsapp/ ) states that it was only for the Android WhatsApp client, and I'm unable to find an update saying that it has been added to the iOS client.
"WhatsApp runs on an incredible number of mobile platforms, so full deployment will be an incremental process as we add TextSecure protocol support into each WhatsApp client platform. We have a ways to go until all mobile platforms are fully supported, but we are moving quickly towards a world where all WhatsApp users will get end-to-end encryption by default."
It seems... unlikely that the crypto integration would be left half-done. I guess I could find a Whatsapp user with an iDevice and another with an Android device and look at the software UI for clues. :D
