Your employees are going to have mixed emotions about this. Some seasoned call center employees will be used to it and this is common practice at many call centers. But some of your employee's are going to feel punished or like big brother is watching (or rather listening) over them. Like most people the first question they are going to ask themselves is, whats in it for me? Some would say its about doing a good enough job and staying employed here! But almost always influence and leadership with fear only yields short term results. You are going to have to make it fun and rewarding for them to embrace it. First make up a scorecard so they know exactly what they will be graded on, no surprises. Next there will have to be some type of reward for meeting the accepted criteria, this is totally up to you. Maybe it is lunch on the company, an extra day or half day of pto, leaving or coming in early by 2 hours. Or maybe you want to do a point system where call center agents can save up for more lucrative prizes, giving them something to strive for, similar to having a long term goal so to speak. Next I have found it is most effective to evaluate 1 call per week with each employee. Reason for this, out of sight out of mind. If you only evaluate once a month, the first week or so after the evaluation the call quality will be high, then after 1 or 2 weeks the agent will loose sight of that they are being monitored.
Call monitoring will really improve the quality of your calls and customer service. Also a cool thing if your employees engage in emails to customers is to randomly select an email from that employee and send it out to all their peers, you would really be surprised what is being put in a lot of your company's emails to customers!