Revelation Online details the many ways to travel the world
Your first ground mount, however, is available fairly early on and will allow you to get from place to place far more efficiently. You also have access to class-specific mounts at level 69 (nice) that can both walk and fly, and there are mounts that carry passengers such as the mount included in the Founder's Pack. So there are some situations where you actually will not want to be flying. It might seem strange, but occasionally being on the ground is a good thing.