With regard to cell-towers: the inverse-square law will underestimate your radiation exposure from a cell-tower, because they are directional and the inv.sq.law

With regard to cell-towers: the inverse-square law will underestimate your radiation exposure from a cell-tower, because they are directional and the inv.sq.law relates only to to perfectly isotropic radiators. In other words: you need to factor the cell-tower antenna gain (typically between 7-10dB) into your calculation.