Is that the one where the guy's sitting alone in a white room and gradually orders all this stuff from the phone book? If it is, then the song you're looking for is LEMONADE KID by late 60's Californian band KAK. It's on their sole LP (also called "Kak") and you should be able to get it on CD somewhere. It's only the first minute of the song that's instrumental and then some vocals come in... weird choice for a BT ad though!