I think a busy London frequency is an amazing thing to listen to. The controllers must start talking in anticipation of pressing the microphone switch, it happens that fast. With everyone on the ball it works like clockwork, its the idiots not listening out that screw it up. I must admit though, when switching onto a very busy frequency, I do sometimes wat to be called rather than force a check in. Is this good practice? To me it does seem to work well. Many times we have been given our next instruction (climb etc..) without the formal check in first. I have no problem with that.