Having lived through the Great Northeast Power Outage of 2004, one thing that struck me was the that some peoples' cellphones stopped working immediately (i.e. couldn't find a tower) and some kept on working throughout the outage. That was 2004: in 2010, with our daily reliance on cell phones and smartphones for communications, one would image that cell towers would as standard practice have power backup to last at least a couple of days. However, this may be over optimistic. In 2008 a proposal by the FCC to require cellular carriers to have 8 hours power backup on their towers (yes, that's just 8 hours!) was fiercely resisted by the cellphone carriers on the basis that it would be impossibly expensive to implement, and was subsequently nixed by the White House.
Of course the most useful information would be to know what provisions different carriers take to keep their sites going in a power outage, but this information seems almost impossible to find. Anecdotally, most towers seem to be active for several hours in a power outage, but this seems to vary widely by region and carrier. There are some encouraging signs for the future though: for example T-mobile just installed their first grid-independent solar powered cellular tower.
Does anyone have any clues on this one? Either experience as a user or actual knowledge of what particular companies' policies are? If so, please leave a comment!