I have found a way to change the font in Notes. If you have a Mac and use the Mail application, you can sync your Notes with Mail using iTunes. Then in Mail you can edit the Notes and set the font as you wish. When you sync back the Notes to the iPhone, Notes font will be changed accordingly.
But if you create a new Notes on the iPhone, the default font remains the same, thus unchangeable.
Also in Mail-Preferences-Fonts you can change the default font for Notes, that changes the view in which Notes are displayed.
These step may also work for iPods and iPads.
