Text Input Mechanisms in Mobile Web Clients
Text input is much more difficult in mobile web clients. One of the things that make mobile web browsing end up with an awful user experience is the problem of typing complex URL in order to access a web site.
This is why entry points to services should be kept as simple and short as possible (see PickingShortUris). Always try to avoid symbols which might take a lot of keystrokes to be typed. It is not easy to establish how hard it is to type a symbol in terms of keystrokes as there is a wide range of mechanisms for text input.
An interesting list of different mechanisms for text input in mobile devices can be found in Little Springs Design web site