The two have shared intimate chats - but when Bono hangs up something very strange happens.
Borrell revealed: "Nobody has Bono in their contacts! Bono doesn't have a number that can stick in contacts. The last time Bono phoned me, it wiped all my saved text messages out of my phone.
He added: "It went 'ching, ching, ching, ching' like that - like a Pac-Man thing. He deleted all my text messages - it was amazing! Maybe he was using Al Gore's phone of some secret service stuff, but there was no way you could get the number to call him back because not only had the number gone but the whole call history had gone. I don't think anyone's got Bono's number."