2G operators leapfrogging directly to LTE can relax about mobility across access networks. LTE is designed to support user movement across 3GPP and non-3GPP networks.
In fact, Motorola has already demonstrated handovers from 3GPP and 3GPP2 networks to LTE.
Operators can also leverage different inter-technology mobility approaches for a smooth migration to LTE by maximizing the use of legacy network coverage.