As I predicted before 4G had even hit the ground. If 4G delivered on its promises (bandwidth, latency) then it would mount a serious challenge on the fixed line market.
Enter: Relish, offering unlimited data with multiple service offerings.
Surprisingly what looks to have given them this ability might be that they are not wholesaling from the big 4 cellular networks and are using UKBroadband's network for 4G instead.
Considering there is no line rental to pay. £20 for unlimited data providing isn't that bad and 1 month contracts are available! At the moment its limited to central London but as UKBroadband's network expands, i'm sure they will as well.
Not to mention that we might start seeing other providers popping up who Wholesale off them. Lets just hope that contention doesn't become a big problem later on down the line when/if their network gets busy.