i've done it quite a few times with girlfriends and friends i've hooked up with. i think it's awesome fun, personally, as long as it's with someone you actually have some chemistry and affection with. i could never just call up a stranger on a phone sex line and do it. when i've had girlfriends go on long extended trips elsewhere or we'd both be talking and really horny with no way to actually get to each other, it made for an awesome substitute...just listening to them while you get them off through your words alone and getting turned on by their words and sounds of arousal. hell, listening to my girlfriend cum over the phone as i talk her to orgasm would usually be enough to drive me over the edge too.

sigh...like all sex, i miss it greatly. :p