If you're including 3 years of service costs, then the phone only costs $100 or so since it'll be subsidized.
And you really need to work that out for yourself. For me, having internet everywhere is worth a lot. I live in a city where I walk around and get lost a lot. If you go to a store and find something is out of stock, your phone can tell you who else might have one, and show you a map of how to get there.
If I'm in one of the large box stores and I can't find a price tag, I just scan the item with my phone and get all the details.
When my internet goes down at home (fucking rogers), I just tether to my phone.
If I need to rent a car, I can arrange a zipcar through my phone, and even honk the horn to help me find where its parked.
There are a million small uses, and to me, they're worth the $30/month I pay for data.