Cost Efficiency

This question relates to the cost efficiency of PoIP, we have a company of about 100 employees, that is spread out across 4 states and two countries, I would like to be able to discuss with, relife implamentation of a PoIP network, and I would like to hear some opinions of whose services are considered the best, whether they be free of commercial I dont care, but if more information is needed I will be glad to give it, also suggestions for other strings would be awsome. Thank you for your time, and have a good day.

Sinclery Robert Mckay