This is an odd little device. It seems you can only call other express chat users? it's reminiscent of cellphone systems from the old old days like Nextel walkie talkies. Also I see its available in India only and given the feature restrictions perhaps it's meant as an ultra low end device ?

If HMD came out with something that was optimized to the nth degree for whatsapp calls, that might be interesting, but even then I wonder how cheap it would need to be to compete with budget androids.

There looks to be an express chat app for iPhone and Android as well.

I assure you it can do regular calls and texting on the public telephony grid.