Do you have more than 5 trucks? If you do then I can recommend a few but, if its just you then you don't really need one.
There are laws that divide Dispatcher and Broker. You can be a dispatcher with "power of attorney" or "bona fide agent"but in order to actually book freight and set up accounts with shippers and multiple carriers you have to be bonded and have broker authority. You get caught trying to be a broker without the proper documents its a hefty fine.
They act as a agent for the carrier. There is a guy on here that has been operating his Dispatch Service over 30 years. I got started in my business using a Dispatch Service. What is illegal about a Dispatch Service. They can operate with or without their own numbers. They can not act like a broker without bond and credentials.
I gather from your answer you do not work for yourself. You can go to the brokering section to find out the definition of double brokering, or you can ask someone who has their own numbers.