I would recommend you to search online for getting phone numbers of companies which provides office space, virtual office and conference rooms at best price.
I also agree that the easiest and best way to look for virtual office service provider is to search it online. For e.g. if you are looking for virtual office service providers in Ohio, then search like "Virtual Office Space Ohio" in search engines.
Virtual offices provide you with everything you need to create a professional corporate image. Virtual office services give you the possibility to register an official business address, without the need to rent out physical office space.
It would be a lot easier to search online for virtual office service providers. You can easily decide that which business provider would be the best according to your needs and requirements.