Yes, being using this free mindmapping app on my iPhone recently to note down ideas and thought in mind map forms.
The interface is so easy to use, simple and interactive.
You will also able to sync up your mind map to mindmeister server where you can later share it with your friends or colleagues.
As mention on the mindmeister website as this post is written, they have few accounts option for you to “rent” their service. For the free account, you will able to sync up to 3 Mind Map with some limited features.
But no worries, without syncing up to the server, you will still able to write as many mind map as you want in your iPhone.