Seoul's subway system has complete cell coverage in all train tunnels, stations, pedestrian transfer tunnels etc. You can literally get on at steet level and exit anywhere else in the city at street level and maintain a call.

Since satellite-to-phone broadcast TV (DMB) launched last year they've added underground repeaters for that too. When WiBro launches here next year, I expect we'll be able to use wireless broadband internet system-wide too.