PBX cost calculator
This was a project for a friend of mine. The plugin calculates the monthly cost of a PBX and any extras you need.
The clever bit is how the sliders update to show the handset and inclusive minutes as you increase the number of lines.
You may not be selling a PBX but you can see how the settings can be customised for your business.
If you want a version like this please contact me.
Note that these plugins are not free. The cost depends on the complexity of the plugin and what changes you need doing.