Boston will soon have prevalent cellular access on the T Central Artery road tunnels (thanks Rob). Due to a deal struck with the Massachusetts Turnpike Authority, Verizon, T-Mobile, Sprint Nextel and Cingular will all have a presence in the tunnel system. Which means Bostonians will soon be able to have awkward, cramped conversations during their commutes.
This is relevant because up to this point, many cities, like Boston, have only had access to one or two providers on their subways. As far as I know, Boston is the first city to access to all the major providers on its subway.
Boston Tunnels get Cellular Service [Mobility Today]