We successfully moved a client from Trixbox to 3CX this week. They were having ongoing call quality and support issues with their system.
Being a very straightforward and small setup we moved them to 3CX during the middle of a working day with virtually no down time on their phones.
We never really promoted the added features of 3CX over Trixbox to the client before installing it, they were just happy to have a phone system that worked and one where their clients could hear them clearly.
One of the added bonuses of 3CX which they really like was the 3CX MyPhone which they have setup on all of their PC’s allowing them to easily see who is on the phone and allows them to setup conference calls (something they do a lot of) very easily. They also use the 3CX Outlook plugins to allow them to make calls with a single click from within Outlook.