If i suspect it is a punting phone ie they have called every so often. I will call the number. My phone is set to withold id. If that phone is always off or no one ever answers it, it is a punting phone.
This is potentionally one of those that will make an appointment and want to come straight away and when he's got your details he will turn the phone off. Mostly single men aged 30 to 50.
I save the number as pf and when this person calls I ask for a deposit.