I have here on the desk in front of me a BT Oscillator 87J. A network tech left it here after checking our line and finding nine (count 'em) faults on it, which have been causing appalling crackle and increasingly dodgy broadband for quite some time now (we used to get 1.5Mb, now we are lucky to get more than 128Kb). Getting him out here is a story in itself, I had to fight VM for weeks to get them to agree there was a fault and call in BTW to investigate.
He left it so when he phones from somewhere down the line tomorrow, Mrs T can plug it in and assist with the diagnostics.
What does it do? I hate having gadgets and gizmos in my house that I can't play with.