Most 2G systems used TDMA, so the phones inside a cell spitted the time between them. e.g. one phone could send almost all the time but 10 phones sent 1/10:th of the time each.

3G and laster used WCDMA (as some US system used even in 2G) for the radio. Where encryption of the data over a wide frequency span makes the signals mix in the air. But at the same time lowering the needed effect to get the signal across. With WCDMA you can send on an effect below the background noise and still get the signal across.

Lowering the effect of the radio is a big goal as it drains battery to send radio signals. An effect you can see it you travels in areas with bad receptions your phone battery drains significantly quicker. The best way to lower the radio exposure is to have loots of radio towers close to people. The alarmists scaring for cell-networks have made some problems in building enough towers, and by there fear of cell-radio transmission they increase the energy transmitted by the phones in there area.