I’m typing this post on my mobile phone, an inexpensive Samsung Galaxy something with a 5″ screen.
After playing around with the WordPress admin interface a bit, I’ll start by saying that most things work absolutely fine. If you are logging in with a specific need to update something quickly or add a post draft then you should manage it without much trouble.
The main hurdle using WordPress on mobile seems to be with plugins and the editor page. Once you have a few extra shortcode buttons it just doesn’t really fit. After creating a new post draft just the act of scrolling down to the editor box while the icons loaded caused me to tap one or two on the way down – leaving me with some accordion shortcodes in the editor. Not at all what you want to happen while editing a complex page or post.
I’m sure most websites have a few WordPress plugins, so this is probably going to be an issue.
Overall, I wouldn’t bother trying to get any real work done in WordPress on a mobile device – building pages or even regular writing would not be easy.
But if you need to, then you can perform small tasks. Things like adding a new user, changing passwords, publishing existing posts or changing taxonomies should not be a problem.