Office phone system with 35 lines?

I am very confused on how this works. I am looking to start a business in sales. I want to set up about 35 lines with different phone numbers or extensions. I would like something that would be unlimited, that way I would have similar monthly charges. What is the best way to go about this? Would it be good to go with those digital phones, which connect to internet lines and offer unlimited national calling for about $50 a line? any help would be greatly appreciated as I am lost. Thanks in advance