Max allowed TX levels (Watt) for some common systems:
GSM 900: 2
GSM 1800: 1
UMTS 2100: 0.126
LTE: 0.250
Power level is dynamically reduced depending on how good connection is with base radio.
Some systems are transmitting in short time slots. Due to this have for example GSM 900 max average power level 250 mW.