Your scenario doesn't equate;
First off the woman using the phone wasn't an unknown simply borrowing the phone to make a random phone call. She had been given the phone expressly to make campaign calls.
Secondly she wasn't using the phone in committing a crime.
To answer your question though, yes, I would be partially responsible. You would be almost certain the police would be looking for me, the owner of the phone, if they were investigating the matter.
I think we've already established that Romney will say anything to get elected, so it's no surprise that his supporters will go even further in that direction, particularly given the ability to establish semi-plausible deniability.
The whole thing is particularly effective and deplorable when preying on the fears & apprehensions of low information seniors using pitches like "Muslim!" "Soshulist!" "Death Panels!" and "Ending Medicare!".
Not to mention that Romney's running mate is the party pushing to voucherize Medicare, then adjust for inflation rather than actual cost increases, while the ACA, Obamacare, closes the donut hole in drug coverage, an enormous boon to many seniors, while strengthening the tax base that supports the whole program.
It's also obvious that none of the handwavers & apologists in this thread have ever worked a phone room, either. You can hear your coworkers making their pitch, and adjust your own if theirs seems to work better. The boss can listen in any time he wants, too, and will critique your performance whether you want him to or not. All he really cares about is results, regardless of how they're obtained. If lying, cheating, stealing, slandering and so forth get results, he's all for it. In the unlikely scenario where you're busted for it, he'll just say you're off script...