Customers usually tend to like companies showing a customized interest in themselves. Therefore, calling by their name (if possible) or showing popups offering free help would be great to maximize the conversion rate.
The popup offers help to the ones browsing on the website for more than a predetermined time (by the company). Also, the customer is informed about that she will be called in 15 minutes. This idea is amusing as well as well-applied on the popup. The design is straightforward, some shades of blue are used, and icons are preferred rather than images.
Additionally, you definetely consider purchasing a popup providing mobile optimization because there are more mobile users than computer users on the net.