07711 911905
From Tardis Wiki, the free Doctor Who reference
07711 911905 was the number used by Martha Jones' mobile phone at the time the Tenth Doctor gave it "universal roaming" and Martha called her mother Francine from the SS Pentallian three times in one day. (TV: 42) By the time she gave the phone to the Doctor, the number had become 07700 900461. (TV: The Stolen Earth)