isdnlog 1:3.12.20071127-0ubuntu6 (i386 binary) in ubuntu karmic

 isdnlog logs all ISDN connections, and can calculate the cost of calls. If
 sufficient data is available, it can even recommend which alternate carrier
 would have been cheaper for a given call. For countries where calls are charged
 per discrete unit, it can disconnect the line just before the next unit starts.