A method of routing call signalling to a destination address from a first cellular mobile communications network comprising a plurality of cells to one of a plurality of smaller cells collectively identified in said first mobile communications network by a single virtual cell identifier. The method involves receiving call signalling for a call in a first routing domain associated with said first mobile communications network, and then determining in said first routing domain from said destination address a forwarding address for said call signalling, wherein said forwarding address comprises said virtual cell identifier, forwarding said call signalling to a network gateway node associated with said virtual cell identifier in said first routing domain, said gateway node being further arranged to participate in a different routing domain by identifying, using said different routing domain, the identity of one of said smaller cells associated with said destination address; and finally, routing the call signalling to said destination address.