The higher the frequency the more 'line of sight' a signal becomes. I don't like to generalize, though in the more affluent countries the public find cell antennas to be an eye-sore, many also assume a cancer risk is present so there is a tremendous amount of lobbying to minimize the number.

Here in Asia there are cell antennas everywhere, including inside most larger buildings. I don't recall ever having lost signal, dropped calls are also quite rare.

Like others have said, don't mess with your antenna without doing a bit of math beforehand. The tolerances above 900MHz become quite important.

I would suggest this is a telco issue rather than anything to do with the N900 at all.

Edit: Apologies amgine, I just saw your last reply, you're not going to do it :-)