Calculate the total time of calls from a phone number

Hi, I would have the total time spent on the phone with various clients, looking into the reports of the CDR I noticed that if I answer a call with phone number 0372987654321 ( my phone number is 03721212121212) from extension 4011 tells me:

01/06/2011 14:49:14 SIP/4011-0 … 03721212121212 03721212121212 0372987654321 ANSWERED 00:20

but if i forward the call to extension 4013 in the log in I get:

01/06/2011 14:49:29 SIP/4011-0 … 4011 “aaa” <4011> 4013 00:22 ANSWERED

so if I make a query in the database do not know to that phone number belongs the record above.

Can I keep the number of the caller somewhere when transferring a call?
Same thing of course also for outgoing calls.
By Obe.