without going into the pros and cons of a wired/wireless system I suugest you go for redcare which is supplied through the bt line and monitored 24/7 by them ,and yes you can use the phone as well as your alarm on the same line without renting another one ...when the alarm goes off your alarm company will contact you first to see if all ok and if not contact the police......the alarm will also trigger at the monitoring station if your phone line is cut or damaged,if you are going for this the company will arrange a bt engineer to fit a redcare block and bring it into service (CHIRPS) but make sure it is terminated on the screw terminals of the main nte so if you take off your frontplate you wont trigger the alarm