Richard,Purplebus,
I would strongly suggest that the evidence of someone using your telephone while you are away is not going to prevent a good claims investigator from establishing that you breached the terms of your policy.
If you were caught out and your house had burned down how much trouble would you be in?
There are policies out there which will cater for your needs and for exmaple they may add a warranty that the property needs to be visited or kept at a certain temperature to keep cover operative.
Richard