iPhone works great over wifi but laptops can't access Internet. What's going on?

The apartment wifi has had problems for a while and we have tried replacing the modem resetting everything called the charter assholes over and we still have issues. Today my iPhone 5 is working great over wifi getting 40 megabits down but my MacBook Pro summer 2012 and my roommates dell and toshiba (just saying that it isn't just one computer, brand or os) all can connect to the router but either can't access the Internet or they get about .01 megabits down. Any advise?