Be aware that you'll need open ports on the routers you find when using wifi... (which means either hacking into the router to open the port or being the admin)
On 3G that will work.
I once used no-ip: you can choose a domain from these:
So your domain will be in the form of you_chose_this.chosen_from_the_list.com
For a mobile use, it's Ok, but to host properly a site i'd discourage doing a home-made server, due all the problems you may have, especially when MySQL doesn't like you.