One request we get fairly frequently from clients that have been brought over to Thirdlane is to have a user-friendly Call History section.
When a call comes in, goes to a hunt group, no one answers and it goes to voicemail the office manager wants to know why it went to voicemail because they don't see that the call went through the hunt group. This is just one example but being able to see the objects between Answer() and Hangup() would make the system better understood by the end user and really help sell it.
In one instance we wrote a cradle-to-grave CDR reporting tool for a client because we were going to lose their business over it. Supporting it is painful and it not being a part of the standard GUI feels unpolished so this isn't a scalable solution we can roll out to multiple clients.