Asterisk and iax statistical data

I’m writing master thesis on Asterisk and it’s usage in small to medium office. As the master thesis includes implementing an IAX softphone, I need some statistical data, like:

  • which is the most ofthen used softphone
  • comparison between the number of Asterisk and other implementations
  • iax softphones comparison, common and missing features

Do you have any idea where can I get such information?