Buried at the bottom of yesterday's WaPo story about the $1.5 billion funding package for Metro passed by the Senate is this juicy tidbit:The bill also includes a provision to improve cellphone coverage in the subway system. Within one year, the 20 busiest underground Metro stations would be required to have cellphone access for all carriers. Currently, only Verizon or Sprint roaming customers can receive signals.The last we heard about plans to build an expanded......