A software program executable on a mobile telephone suitable to cause said telephone to interrogate a distant recipient telephone by means for example of JTAPI to determine whether the recipient telephone is turned on or not. In a case where it is determined that the recipient telephone is turned on, an SMS message is sent to the recipient telephone. In a case where the voice connection cannot be made it is determined that the recipient telephone is turned off, and a further attempt to make a voice connection is made after a predetermined period. Further attempts are made repeatedly until it is determined that the recipient telephone is turned on, and an SMS message is sent to the recipient telephone, or until sending of the SMS is cancelled by a user.