Getting iPhone cheaper than paying internet?

I've been looking into getting an iPhone and just use the wireless internet off that. I know the iPhone has a setting where the phone can give off WiFi so I could use it on my laptop too. The iPhone costs $30 more a month than the original plan I have now. I'm just wondering if I cancel my phone (house phone) and internet bill to just cable (I had the optimum triple play - so I would have IO cable) then maybe I'd be saving money, and get what I would rather want in the long run? I guess what I'm basically asking is, is paying $30 more a month cheaper than paying for my phone and internet?