120 Underground Wi-Fi hotspots will erupt in 2012

Access will not explicitly be for voice - we asked about VoIP (Voice over Internet Protocol) however didn't get a clear answer. And access is to the platform edge only, not onboard trains.

The state of most of the underground network

Given the state of most of the underground network, voice calls would be impossible in any case. The 19th century network is going through another of its endless upgrades - even TfL's press emails come with a boilerplate warning of disruptions and delays.