Technically, it doesn't go anywhere. Pick out an Equal Access Provider that waits a fucklong time to do their billing (some don't bill the first month but wait a month or two for the charges to get billed) and let it die eventually... What'll happen is that the switch will have a record of the phone as a residential class but the billing systems won't really know the number since it will be a resold number (if it's a COCOT) or originally a line-class that wasn't in the billing computers in the first place (if it's BOC-owned). There will be some confusion and it'll eventually get found out, but it'll take some time. Most likely when stuff like this happens it's put on the switch staff as a mistake in ordering procedure (yes, a *mistake*)... Things like this used to (ahem) happen all the time "by accident" in New York and other places I've been to; random payphones would make free local calls for a while and eventually go back to being payphones... I've seen the resultant email parried about by provisioning staff and the like -- it's amusing.
And then where does the bill Go for 10 10 XXX?