tnpbx

If you need reports on the DN you will need to acquire it in symposium. Yes the PBX has basic CDR and you would have to turn it on for your routes and spit it out a TTY port. It just spits out raw data that you would then have to interpret.

Kalahary-Harry

Default Symposium reports give the data combined in 15 minute intervals, and in the case of CDN's / DNIS's it reports on incoming calls only. If you want full details you have to activate your Call-by-Call (log on to your SMI Workbench, Historical Reporting properties / config). You need to specify exactly what call by call statistics you want. Beware, takes up lot's of disk space. To read the data you have to import it into excel via OBDC, then you sit with a huge spread sheet full of data. A call can be broken into different segments, depending on what happend to the call during it's life. I found those stats only useful to investigte a particular call like a serious complaint, not for general statistics (way too much data to sift through on a dayli basis).
Are you not using any call accounting software for your extension users at all? That would be your most efficient long term solution. CA software connects to your PBX's CDR port, collects the raw data and puts it into it's own data base. Most CA software reports out bound traffic per extension. In your case, you enter the ACD-DN (the PBX will in any case list that DN 1234 called 555-1234), then you get the info you want, including the cost there of.

There have been a number of posts regarding call accounting software, what they are called, where to get them and so on.
If you already have OTM, you could consider adding the billing module, else look around for software like RSI Telecost's Shadow CMS etc.