The coverage will come from the inclusion of a Wireless Multiplex Terminal systems in certain relay support vehicles. The WMT uses a mix of 4-8 SIM cards from different 3G operators to transmit video through 3G's expanded data channel. Having multiple cards, along with a software-based parsing system (called Continuous Picture Technology), provides a reliable and stable video connection, even while on the move. Mixing cards from various 3G service providers also allows coverage to be maintained throughout varying mobile coverage conditions. While the article doesn't mention specifics, the WMT device can accept video through cables from cameras, or can be connected to other systems accepting wireless video feeds.
WMT and similar systems are becoming the preferred solution for live remote news coverage, as they offer a more flexible and increasingly more cost-efficient alternative to satellites or microwave uplinks.
Source - BBC to capture Olympic Torch Relay live with Mobile Viewpoints WMT, Broadcast Engineering