As a bit of a follower of David Hockney, as far as I am aware he is still using Brushes, and it looks like you can export your drawings to the iPad/iPhone camera roll and access them as you would any photograph.
"When you’re finished with your masterpiece, you can save it in the Brushes gallery so you can easily work on it some more or show it to your friends with the Brushes built-in slideshow. You can export finished pictures to your iPhone’s Camera Roll or use the Brushes built-in Web server to view or download your creations over Wi-Fi with any Web browser on any computer."
iPhones took the world by storm in 2007 and they haven't stopped wow-ing the pants off us yet. We've got handy articles to help you get the most out of this iconic smartphone.
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edit: to amend this it seems that Hockney stopped using the Brushes app, in 2016, after changes they made "ruined it". He now uses a custom written app (by a mathematician in Leeds) which apparently is more like the original Brushes, which he still calls Brushes, but it isn't the Brushes you can download. !