WhatsApp has had a version of its app for iPhones for some time now. However, it is not compatible with the iPad. As may sub-types of the tablets - inclusing the iPad Mini, iPad Air and iPad Pro - have variants with SIM-card slots, this may come across as unfair to some who have bought these models.
It is possible to use some workarounds to address this discrepancy, however. One example is loading WhatsApp Web onto Safari, although this may require an iPhone for activation. Then again, it would be desirable (and possibly more convenient) to have a tablet-optimized, official, iOS solution for this app.
WABeta.info, a site that follows in-development WhatsApp versions, has claimed to have dug up what is most likely a new beta for this very prospect. As you may expect, the work that appears to be underway revolves around the accomodation of landscape mode on the iPad. However, the site also claims that calls and messaging work on this beta, in addition to Touch ID-linked authorization.
Therefore, those who want to stably IM or phone people using WhatsApp on their particularly expensive iPads may be in luck soon.