A wireless communication device for use in a cellular network. The device comprises a radio interface for enabling communication between the device and a base station of the cellular network over a radio link, and a transfer entity for exchanging user data packets with a core network node of said cellular network over a signalling connection within a Non Access Stratum, via said radio link. The device further comprises a data transmission verification entity for using a verifiable acknowledgement, received from said core network node over a signalling connection within a Non Access Stratum, to confirm delivery of a user data packet sent to the core network node over a signalling connection, the data transmission verification entity being configured to selectively include with a user data packet sent to said core network node across a signalling connection, a request to return to the device a verifiable acknowledgement for the sent user data packet.