The Truvelo ones you mean (quite high up)? I'm seriously considering investing in a Road Angel now, as while the Tom Tom is OK, it doesn't beep to warn me I'm over the limit, and I'd rather not spend more time looking at the satnav screen or my speedo than the road :S
Have you looked at the software updates for your tomtom, mine (a go 500 (I think)) beeps at me if I go over the limit, it was a feature put in fairly recently.