Longest shift on phone?

Out of curiosity, whats the longest stint on the phone anyone has seen a girl do? On a channel I mean, not how long your gf or wife can tie up the phone for.

I think the longest Ive seen is girls doing about 2 and a half hours without a break, which I think is pretty good going for keeping concentration. A friend told me there were often stints far longer than that in the "old days" though, so its got me wondering.