Many cell phones have two signal strengths: 0.6 watts and 3 watts (for comparison, most CB radios transmit at 4 watts). (sideband CB radios 12-20 watts, and some illegal 'kickers' to CB radios can transmit 100 or even up to 1000......if you ever hear voices you should not be hearing coming from your home phone, AM/FM radio, TV (before everything was digital), audio speakers, baby monitor, etc. it could be someone on a CB radio with an illegal kicker (or antenna is poorly grounded).
Cell phone Towers transmit 10 watts, sometimes 50 in urban areas.