Our parent company has a product called Erlang for Excel. More information is available at http://www.erlang.com/excel.html which is very popular, easy to install and accurate.
I’m interested in the differences between the various online calculators you mention. We think that our calculators were the world’s first on the Web (launched in 1996), and we think they’re accurate.
Lastly, Erlang B and Erlang C are modelling different situations. Erlang B assumes that all blocked calls clear a system immediately. Erlang C assumes that blocked calls queue for resources and so remain in the system until they are handled.
Best regards,
Voice over IP Calculator Webmaster.