I would suggest that there's quite possibly an oil starvation problem to the turbo. It certainly should be looked into, otherwise you'll just keep blowing turbos. As I say, normally they are very reliable. To go through 3 in such a short space of time is definately not right.
I would take it to fiat/fiat dealer and explain the history, as this should ring alarm bells with any half decent Tech and they should carry out some investigation into what exactly is causing the turbo failure. This is not normal, and as i say, if its just replaced again, I would expect it to go again as i feel there is an outside fault causing it.
Alan