Unless one is very close to a phone mast, the RF exposure can be much smaller than that from mobile phones and other technologies we encounter at much closer range. As result, it is difficult to carry out epidemiological studies on populations exposed to mobile phone masts, as it is unlikely that this is the only exposure to RF radiation that most people will have. The telecommunications companies and regulatory bodies claim that the exposure from a mast is so low in comparison to a mobile phone, that the RF radiation could not possibly be harmful.
However, some studies initiated by GP practices concerned about the symptoms reported by their patients, have shown a consistent pattern of ill-health effects reported by people living near masts, when compared with those living further away.
Radiation from a cell tower is continual and living within 300 to 400 meter radius could be dangerous (See: http://www.emf-health.com/articles-celltower.htm). Note that poor signal reception on your mobile phone may be misleading because it may be low for one provider but high for another. Relying on visual inspection is also difficult since some cell towers are concealed (tree towers, church steeples etc.). The best way is to check with a meter or have a survey done. Additional sources of external radiation can come from the neighbours next door, e.g., if they have a WiFi router or DECT cordless station on the other side of the wall.