Another small feature that will be available in Roundcube 1.3. An option to display QR code image that consist a (limited) contact information. So, you can quickly share contact with any mobile device.
It looks there are a few standards for this, but I choose the well-known vCard format as a data encapsulated by the image. Many decent applications for mobile devices actually support this method. Let me know if this works or not for you.