You could add however many CS people you need to handle the extra load and then rotate some of them (not all may be suitable for this - pick the extroverts) int

You could add however many CS people you need to handle the extra load and then rotate some of them (not all may be suitable for this - pick the extroverts) into answering pre-sales inquiries, say one week out of four. If I phone you already thinking I am interested in your product and talked to someone who sounded deeply knowledgeable about the service, this would increase my confidence level more than if I talked to a smooth-talker (obviously not knowing your niche this may not apply). Fundamentally I think you need to listen in on some of the phone calls your sales people are taking. What are your customers looking for at that stage? Do they want to talk about pricing a lot? Do they want to discuss functionality or ask about future features?