for all my calls to be routed via the internet; and all yours, and yours, and his, and hers, and theirs and..............Ooops, there goes a huge chunk of available bandwidth.
Picture the scene, it's Christmas morning and you fancy a quick login to the forum to wish me and Mrs.FE and Grandma FE and all the little FEs the compliments of the season (next Christmas will be our fifth online). Only you can't do that, because you're cooking the turkey, and you can't afford to wait ten minutes while each page loads. Half the planet is on the internet, calling the other half using VoIP, and there's a festive digital punch-up over the last vestige of bandwidth.
Or am I exaggerating just a smidge?