Being asked to enter your nickname can be annoying, especially on the iphone/ipod touch. Moreover, you also need to worry about having a language filter.
Instead of asking for user input, you could use something like anonymous-1, anonymous-2, etc... but that's not very interesting.
Another possibility is to generate fake names, but getting the gender wrong would be annoying to the player.
Another idea is not to use text at all, but visual images generated automatically such as these:
http://www.idiom.com/~zilla/Work/VisualIDs/visualids.html
