I'm using Roundcube Webmail from last 2 year. Recently I updated my Roundcube Webmail version. When I go through the Roundcube Webmail Forum I got to know there is mobile skins are available which are compatible with latest version of Roundcube Webmail. I purchased Royal-Blue Mobile Roundcube Skin from www.roundcubeskins.com. Awesome work done.
This is an awesome webmail client, but I personally prefer Squirrelmail :)