A perturbation is made to contents and/or locations in time and frequency of Reference Signals (RS) transmitted by a cell, such that the perturbation implies information regarding a capability or configuration of the cell as regards availability or configuration of a network functionality, for example facility to offer a narrowband virtual carrier operation. The contents and/or locations in time and frequency of the reference signals used are typically based on the physical cell identity (PCI). In certain embodiments the PCI carried by some identifiable RS resources is changed: in others, the RS is transmitted in unexpected resources. The network functionality configuration information is inferred from the various relationships between these transmissions and the cell's actual PCI and/or expected RS transmission resources.