Two Nokia N900 phones have been hacked to give them the ability to provide an extra sensory dimension to phone calls, allowing users to send touch messages while on a call.

The ForcePhone prototypes were constructed by the Helsinki Institute of Information Technology in collaboration with Nokia Research, to investigate the potential for haptic communication options.

Both devices offer users the option of squeezing the handset during a call to trigger a vibration in the paired receiver, referred to as a pressure message.

The technology works by incorporating a force-sensitive resistor into the edge of the handsets, which connects to a sensor board in the phone’s microSD port. The resistor is capable of recognising four levels of pressure and triggers a corresponding intensity of vibration.

Three couples in long-distance relationships trialled the ForcePhones and tested out a range of pressures; from angry squeezes (designed to irritate partners during a row), to more affectionate touches.

Despite initial testing, there are  no plans to integrate the technology into forthcoming Nokia handsets.