What is the TARDIS's phone number from the british tv show Dr. Who?

Origingally, the TARDIS, while being a police box, didn't actually have a phone that works. The phone in the little box at the front, behind the sign that says

Police Telephone

For Free Use of Public

Advice and Intelligence

Obtainable Immediately

Officers and Cars Respond to Urgent Calls

Pull to Open

doesn't actually work. It isn't connected to anything. We do see it ring in the episode the Empty Child, and the Doctor (Nine, at this point) is entirely shocked, because it isn't a phone.

However in the redesigned TARDIS in Series 5, it now has a working phone on the inside. The Doctor receives a phone call on it from Winston Churchill. However the number itself is not known.

It rings again in Series 7, 'The Bells of St John' - the phone is in fact the titular bell, close to the TARDIS' St Johns Ambulance logo.