What is the difference between a Carrier, Agent?

Carrier:
Technically any company that can sell you the service and then bills you for the services including taxes is a carrier. There are many companies that will buy the service from somewhere else include the taxes as a cost of goods then mark it up and bill you a flat rate. Be cautious if you don’t see taxes on your invoices. It is not that you are a good guy; it is probably they aren’t registered to collect, or sell the services.
Here are a few examples of carrier designations and a wiki link for more detail.
