Sky’s long awaited MVNO (mobile virtual network operator) venture has finally arrived, built around the O2 Telefonica owned network, unveiling features of its new mobile data plans that it hopes will throw a spanner into the works of the UK mobile market. Rival mobile operators may be breathing a sigh of relief at first glance, as Sky Mobile’s debut has not been as aggressive as first feared, but the MNOs in mainland Europe will be observing Sky Mobile’s operations like hawks, in preparation for its inevitable invasion on Italian and German soil. The key feature of Sky’s new mobile plans is the ability to save unused data for up to three years, to be redeemed at any point in time…