By the time of my second arrest during the 1996 Democratic Natl. Convention I was prepared. Pocket full of change, and the #s for reporters on my arm, and I'd made friends with the booking Seargent. Alas, I discovered that all the phones connected to the special exchange Ameritech had created for Convention activities could not be reached from pay phones.
"We are unable to complete this call as dialed..." ad infinatum. Got the same result afterwards from payphones on the street.
Don't count on your cellphone either. As they raided and closed the Weedstock Festival in rural Wisconsin last memorial Day, the authorities were able to selectively disable both analog and digital cells in use by event organizers. My hunch, this was a dress rehearsal.