same question i 've get searched by app store with No result  

I think it would be good if it had an app for iphone and ipad etc, also I think its notebook feature should be improved to make highlighting errors the default setting as doing it just via comments is hard to spot sometimes where the error is

This is quite old question, but I found this:

http://support.italki.com/hc/en-us/articles/216563737-Does-italki-have-an-iOS-app-for-Apple-products-

It says it's under development.

It's a great pitty. I would like to talk my friends any time through my phone.