Currently, Olark start to charge if you want use their service. They have the right to do that and that is a good thing. However, if you do not want to use Olark, we have a new live chat plugin with 100% free. You can try to register and download the package here: http://zucando.com/zen-cart-modules/other-modules/the-100-free-live-chat-application-for-zen-cart 

Increase your conversion rates by keeping in contact with your customers with this lightweight, feature rich live chat widget by Olark.

The Olark Chat Widget works on all pages (SSL and non-SSL) and connects to most major desktop chat messenger programs including Google Talk. The single piece of JavaScript added to your website will allow you to see what customers are doing on your website and give you the ability to message them at any time. You can even message the customer when you see them having problems completing a purchase in your store!

Olark also integrates with many CRM platforms and Help Desk software. With its reporting functionality, you can tell who your customers are, the most active times of day on your website, and even track how well your operators are performing.

Customizing Olark is simple with multiple themes and options to choose from to get the widget looking just right.