Zopim offers a great way to add a text chat window right into your small business websites with their free Zopim Lite. While the customization features are limited in any Lite product, it is fully functional and doesn't have the 30 chats per month limitation found in ClickDesk Free.
The problem is that, on mobile phones with really small screens, even the minimized chat bubble can take up a significant portion of valuable screen real estate. If you happen to tap it, the minimize button may actually end up beyond the top of the screen disabling people from accessing your site. To make matters worse, a cookie will keep re-opening the window each time you reload the page.
Here is an example of the code which will disable Zopim on screens with a height or width resolution under 480 px. I've highlighted the two lines that you will need to add to your code: