Just clarifying... this is the percentage of calls that are answered, so you are looking to reduce your abandoned rate?
This is directly related to seconds to answer. So improve your service levels/seconds to answer and abandoned rate drops.
What your customers are used to also plays a big part in this... if you have had a 90%/10s service level for the last 5 years and you suddnely change it to 60%/40s then you will notice a major increase in abandoned calls, more than what you could expect in a call centre switching from 70%/30s.
I found that the expetations of our Hong Kong and Asian callers was much higher than our Australian callers so traditional metrics for abandoned rate just did not apply.