that happened to me during my marathon, too - several people around me was either a) talking on cellphones or b) taking pictures all over the place with a digital camera! but using a cellphone really is the best way to ensure that you can see friends and family during the race course, and seeing friends and family during the race was the only reason i didn't fall over and die in a miserable lump of a person.
There is the school of thought that says that a distance runner should never pace oneself so fast that s/he can't carry on a conversation while running. That certainly helped me get through my first 5-miler last year. I did think that that was a rule of thumb, however, and not a hypothesis to be tested with a cell phone.
Would it be okay if they were just reading/commenting on blogs?
Its just like Nascar. You need to stay in touch with your crew chief. And your broker.
One of my commenters did half-jokingly suggest moblogging a future marathon. Unfortunately -- or fortunately, as the case may be -- my cell phone (a) weighs way too much to run with, and (b) is cameraless. So that's definitely not going to happen. But I've got to admit that, while annoyed by all the yakking going on around me, there were two moments when I really could have used a cell phone: one at mile 13, when I wasn't sure where my posse was going to be, and one in the so-called "family reunion" area, when the phrase "needle in a haystack" kept going through my mind.
On the other hand, if I'd had a cell phone, there'd have been a massive temptation to call a cab around mile 20...
The best one, though, was the guy who I overheard saying, "No, I'm running right now." I really wanted to know what the question was that prompted that answer…
The question was:
Are you an obscene phone caller?
Actually, I bet the question was "why are you calling me/answering the phone? Is the marathon over?"
"No, I'm running rigiht now."
"Oh. Then why are you talking on the phone, idiot?"
At least, that's how I hope that conversation went.