I suppose I should defend slightly what the guys are doing, I would say in the vast majority of times the engineer is not cutting off one customer to feed another, at least not in his eyes. He sees that as a spare and uses it, quite often his system will be telling him it is spare but the records are wrong. This doesn't excuse poor engineering practices of course.

Sounds like your common problem is the card locking in the exchange, the very fact that they remote test it will likely free it up again and bingo it starts working. Do you find it happens on the same brand of router you are using? If so it could be some kind of conflict with certain cards, and that is what is causing the locks? That is the sort of thing we used to see back in the early days where people didn't like using the BT supplied router and put their own on there.

Cheers

Cris.