1. In medium/large call centers in the US (or world wide) (50+ customer
service agents),

a. What is the average cost per email interaction (i.e. agent responding
to customer email?). How does it compare to a phone interaction?

b.  What percentage of inbound customer email turn into sales leads/
opportunities?

I have a couple of estimates for the first question.

http://www.callcenternews.com/resources/stats_size.shtml
The average cost of handling a call in a telephony-based center ranges from 
US$50-74, 
and the average cost falls 43% in a web-based call center.

Nortel, citing statistics by Forrester Research, 7/99.

http://www.incoming.com/industryfacts/performance.html
According to supportindustry .com and Help Desk 2000, the average cost per 
call for 75% of the support organizations they surveyed is $25 or less. 
The analysts expect this cost to fall to $18 per call within three years as a 
result of e-support technologies. 
(Cited in Call Center Management Review, November 2000, www.ccmreview.com )

http://www.callcenternews.com/resources/stats_misc.shtml
Cost of a typical telephone call: $2-5 each. Cost of a typical web transaction: 
$.25-$.50 each. 
One live call = approximately 10 web transactions.

Alltel, presentation at ICCM, 1998.


http://www.benchmarkportal.com/newsite/article_detail.taf?topicid=19
Is there any data on the cost of answering a customer's inquiry by phone, e-
mail, 
fax, regular mail and through on-line self-help? 

Answer

We have polled call center managers and Webmasters, and have averaged their 
results across industries as follows: 
a) telephone=$3 to $4 per inquiry, b) e-mail = $15 to $20 per inquiry, c) fax = 
$25 to $35 per inquiry, 
d) regular mail = $25 to $35 per inquiry, e) Web site = $0.50 to $1 per 
inquiry. 


I could only find one estimate for the second question:

http://www.callcenternews.com/resources/stats_size.shtml
$700 billion in products and services were sold through call centers in 1997 
and this figure is 
expanding by 20% annually.

GeoTel citing Telemarketing Magazine, 9/98.

According to www.lefo.ro/iwlearn/pdf/gnp.pdf, World GNP (total products and 
services sold) in 1997 was 
approximately 19915669000000, thus the percentage of goods and services sold 
through call centers is
3.514820416025191 (my own calculation).

You may find more information by browsing sites listed at
http://directory.google.com/Top/Business/Industries/Telecommunications/Call_Cent
ers/

or searching Google for "call center statistics OR metrics".

Thank you